Adding nutrients to the ocean so tiny ocean plants remove carbon dioxide from the atmosphere is an idea that people aren’t used to. Unfamiliar ideas make us uncomfortable. That gut level “I’m not so sure about this” is natural enough. It comes out as an inchoate sense that such a thing must be risky, that we’ve never done it before and so couldn’t possibly know what the consequences would be.

It’s not true, though. We have quite a precise understanding of what happens when you add nutrient-rich minerals to nutrient-poor waters. Dozens of natural experiments have settled the question. Because nature puts minerals into the ocean all the time, all around the world, through many different mechanisms. And it’s been doing so for millions of years.

Volcanoes do it. Wildfires do it. Even educated whales do it. Dust storms and icebergs do it too. And because satellites have been measuring the ocean’s color with minute accuracy for over twenty years, and research ships have been chasing these events with sensors and sample bottles, we have a large and growing record to show what happens when nutrient-starved water suddenly gets fed. It’s one of the best-documented cause-and-effect relationships in ocean science.

Remember, most of the open ocean is a desert. The top layer of water gets plenty of sunlight, but as you get farther from land the tiny drifting plants that form the base of the marine food web — phytoplankton — run short of one or two key ingredients, usually iron, sometimes nitrogen or phosphorus. Give them what they’re missing and they multiply, sucking carbon out of the air in the process. Take the nutrient source away, and within weeks the effect fades. The pattern has been observed over and over, in different waters, driven by different processes, sort of everywhere.

Tonga on my mind

One case of particular interest to me comes from the subtropical South Pacific. It had long been hypothesized, but never proven, that shallow undersea vents near Tonga might be leaking iron-rich fluid close enough to the surface to reach sunlit water and feed nitrogen-fixing bacteria.

Then, in 2019, a research cruise went and found it.

A single string of undersea vents feeds a patch of ocean the size of Germany with enough iron to fuel a bloom of nitrogen-fixing bacteria that grew two to eight times faster than those in the surrounding water, and pulled two to three times more carbon down into the deep ocean. That work was published in Science in 2023. Follow-up cruises mapped exactly how sharply the iron levels spiked near the vents and faded away with distance, tracked the plankton response cell by cell, and even built a nitrogen budget showing that in some seasons, nearly all of the region’s biological productivity runs on vent iron.

The Tonga-Kermadec range isn’t unique, either. Similar iron-fed blooms have now been traced to volcanic ridges south of Africa, near Antarctica, and scattered across the Pacific seafloor — some fed by iron plumes that drift over a thousand kilometers before they’re used up. One recent study even linked the strength of a Southern Ocean bloom, year by year, to how many small earthquakes had recently shaken the nearby volcanic ridge: more quakes appear to be related to more iron release, which leads to more phytoplankton growth.

All we are is dust in the wind

But in fact, undersea vents are a little niche; the best-known natural fertilizer delivery system is dust in the wind. Every year, wind lifts millions of tons of fine soil off the Sahara and carry it out over the Atlantic; the same thing happens with dust off the Gobi desert blowing over the North Pacific, dust off Patagonia settling onto the Southern Ocean, and dust off drought-stricken southern Africa reaching all the way to Madagascar. Scientists have been measuring these sorts of events for decades: wherever iron-rich dust lands on iron-starved water, phytoplankton growth follows, often within one to two weeks.

Maybe the clearest evidence comes from robotic ocean floats that happened to be sitting in the North Pacific when a Gobi dust cloud rolled over them in 2001. The floats measured the living carbon in the water nearly doubling within two weeks. A dust storm over the Arabian Sea in 2012 was followed by a nearly fivefold jump in chlorophyll. A 2024 study using over a decade of ocean-robot data concluded that nutrients from dust currently sustain roughly a third of all the plant growth happening across the entire Southern Ocean each year — and that during the last ice age, when the world was far dustier, that figure was closer to two-thirds. Deserts, in other words, have been fertilizing oceans on a hemispheric scale for as long as there have been deserts.

Ashes to ashes

Volcanic ash shows these events in sharp detail, because the nutrient additions are sudden, violent, and easy to date them precisely. In August 2008, an Aleutian volcano called Kasatochi erupted and dropped ash across the Gulf of Alaska. Within days, satellites picked up one of the largest phytoplankton blooms ever recorded in that part of the Pacific. When Iceland’s Eyjafjallajökull volcano — the unpronounceable one that grounded European air traffic back in 2010 — dusted the North Atlantic with ash, research ships sailing under the plume measured a spike in dissolved iron and ran shipboard experiments showing the ash was actively feeding the local plankton. The same thing happened after Hawaii’s Kīlauea eruption in 2018, when ash carried more than a thousand miles out to sea triggered what may be the largest bloom ever observed in that stretch of the Pacific, an area of ocean roughly five times the size of Taiwan. It happened again around a small Japanese volcanic island in 2020, and around a Mariana Islands volcano in 2003, in one of the most nutrient-poor patches of ocean on the planet.

It’s not just that researchers have watched these processes from space. They’ve collected ash samples from more than a dozen different volcanoes and dunked them in seawater in the lab, measuring precisely how much iron dissolves out of each kind of ash, and how fast. The relationship between iron addition and primary productivity is now understood in minute detail.

We didn’t start the…

Perhaps the most striking recent example doesn’t involve rock at all. During the catastrophic 2019–2020 Australian wildfires, smoke carrying iron-rich ash drifted out over the Southern Ocean, and set off a bloom so large it showed up clearly in satellite images across a huge swath of open water south of Australia — one of the biggest phytoplankton blooms scientists have tracked with modern instruments. It didn’t fade quickly, either: follow-up studies found the bloom kept feeding itself for the better part of nine months, as the ecosystem recycled the iron it had been given rather than using it up and going back to starving.

Smoke from Siberian wildfires has been linked to an amplified plankton bloom near the North Pole. Smoke plumes from Canadian and other boreal fires are the subject of ongoing research into North Atlantic nutrient addition
, with one modeling study projecting that as wildfires become more frequent under a warmer climate, they could boost that ocean’s plant growth by up to a fifth each year. Even California’s 2020 wildfires left a fingerprint on coastal waters near Monterey Bay, shifting which types of phytoplankton were most common. Chemists have also figured out roughly why wildfire ash is such potent fertilizer: the iron in ash from burning is in a form that dissolves more easily in water than the iron locked up in ordinary windblown dust.

From the deep

A handful of small, remote islands in the Southern Ocean — Kerguelen, Crozet, South Georgia — have been especially intensively studied. They sit in water that would otherwise be as barren as the open ocean around them. Seafloor sediment near these islands leaks iron continuously, and ocean currents smear it out for hundreds of kilometers downstream, producing blooms that come back reliably every single summer. Research teams have spent whole cruises comparing the fertilized water next to these islands with the barren water just beyond it, and the differences are large and consistent: more plankton, more carbon sucked out of the atmosphere and buried in the deep sea, and — in the case of Crozet — measurably more life on the sea floor itself, thousands of meters down, feeding on the extra material raining down from above.

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Icebergs do something similar. A landmark 2007 study followed two free-drifting icebergs through the Weddell Sea and found each one trailed a halo of enriched water, extra plankton, extra krill, and extra seabirds for miles around it, as rock dust trapped in the ice thawed out and fed the surrounding sea. Giant icebergs, satellite studies suggest, may supply the iron that feeds the phytoplankton that accounts for as much as a fifth of all the carbon the Southern Ocean buries in a given year.

A whale of a time

And then there are the whales. It sounds almost like a joke, but it’s very well established that baleen whale poop carries iron concentrations ten million times higher than ordinary seawater, and Antarctic krill populations collectively hold something like a quarter of all the iron floating in Southern Ocean surface waters within their range. Whales and krill are, in effect, a living fertilizer pump, recycling iron from the deep sea back up to where plankton can use it — and some researchers now suspect that a century of industrial whaling may have quietly throttled Southern Ocean productivity by removing a big part of that pump.

Putting it all together

Let’s stand back and evaluate. Even though the mechanisms are wildly different — an underwater volcano is nothing like a dust storm, which is nothing like a burning forest, which is nothing like a whale — they all produce the same basic result: iron-starved water, given iron, grows more phytoplankton, fast and visibly.

This happens on every scale imaginable, from a single ashfall lasting a few days to a chronic, decades-long seep near an island that shows up in the record every single year. And it happens everywhere you look: the North Atlantic, the North Pacific, the Mediterranean, the Arabian Sea, the tropical Pacific, and especially the Southern Ocean, which seems to collect nutrient-addition events from every direction: dust from three continents, ash from island volcanoes, smoke from wildfires, mineral-loaded ice from glaciers, and even whale shit all seem to have broadly similar effects.

So we’re not talking about some wild new speculative hypothesis or an odd-ball observation from a single contested study. We’re talking about the accumulated output of hydrothermal cruises, dust-tracking satellites, floating ocean robots, sediment cores that reach back through ice ages, shipboard chemistry experiments, and decades of chlorophyll imagery. The core relationship — feed iron-starved water, and it grows more phytoplankton, in proportion to how much you feed it, and then stops when the nutrient addition stops — is about as well-established as anything in ocean science gets.

That last point deserves notice. Reversability is a key criterion for ecological safety. You want to be sure that if the intervention you’re pursuing turns out to have a negative effect, you can stop it. You wouldn’t want to risk shifting an ecosystem into a new permanent state. Here the evidence is especially clear. Phytoplankton grows as long as you keep feeding it. When you stop feeding it, it stops growing.

But that’s almost academic, because there is just no evidence of any harm that would need to be reversed. Across dozens of studies on all these sorts of natural experiments, nobody has found any evidence of ecological harm. If you squint, you could say there’s some evidence that in nitrogen-deprived areas, fertilization differentially halps nitrogen-fixing bacteria, but it’s hard for me to see that as a harm: you want to favor the bacteria that fix nitrogen, because they’re the ones that clear the nutrient bottleneck for everything else.

That that’s the closest the literature comes to finding a harm tells you all you need to know. By now, if iron addition was associated with actual some bad outcome —a harmful algal bloom, say, or some kind of toxic nutrient overloading— scientists surely would’ve noticed. But no such thing has been found.

So that gut level sense that we have no idea what might happen if you add iron to iron-starved waters is grounded in ignorance. We have a pretty precise idea what happens when you add nutrients to a marine desert, because we’ve seen it happen again and again all over the world.

In reality, any program to intentionally add nutrients to nutrient-deprived oceans would be considerably less dangerous than any of these natural analogs. Fires, volcanoes, icebergs and vents just dump crap into the ocean willy-nilly, with no plan, no environmental monitoring, no environmental impact assessment, nothing. Nature does this in precisely the kind of blind, reckless, unthinking way that skeptics fear in people, and even then there’s no evidence of harm.

Of course, a program to deliberately increase phytoplankton carbon removal would be infinitely more careful than random geology. It’s hard to figure how intentional nutrient addition carried out under intensive, carefully pre-planned ecological monitoring could be more dangerous than just randomly putting crap in the sea like a volcano does. Thinking it would be is just a sign of anti-human bias.

Which is the point, really.

We have many good reasons to think adding nutrients to the ocean is safe, and very good reasons to believe allowing climate change to run on unchallenged is unsafe. The only thing holding us back is a kind of ideological commitment to the idea that human beings always only get everything wrong, while the random acts of geology are by definition “natural” and therefore good. That’s an ideological argument, not a scientific one.

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Durably pulling a ton of carbon dioxide back out of the atmosphere has the same climate impact as never having emitted it in the first place. The sky doesn’t keep track of why a ton isn’t there. For climate policy, a ton of CO₂ you’ve durably removed is the same thing as a ton of CO₂ that you avoided emitting in the first place.

This isn’t some fringe position. The IPCC’s Sixth Assessment Report — the most heavily scrutinized document in all of climate science — says that “the deployment of carbon dioxide removal to counterbalance hard-to-abate residual emissions is unavoidable if net zero CO₂ or GHG emissions are to be achieved.” The discourse treats carbon dioxide removals as somehow different from reducing emissions; the science doesn’t do that.

So if a removed ton equals an avoided ton, and if the money the world will actually spend on climate is finite, the whole problem boils down to one question: how can we do this cheapest? If we think about it logically, spending $100 to lower carbon emissions from shipping by one ton, say, only makes sense if capturing carbon dioxide costs more than $100 per ton. If we had a $50 ton of removals, then insisting on spending that $100 on abating shipping emissions would have the net effect of leaving one more ton of CO2 in the atmosphere than needed.

Climate discourse ought to center how much keeping carbon out of the air actually costs. A method’s cost is set by physics, and every approach has a cost floor, because you can’t negotiate with the laws of thermodynamics. The cheap pathways piggyback on free shit: sunlight, photosynthesis, gravity. The expensive ones need lots of expensive power, or land, or machinery, or all of the above.

So where are those cost floors? And why?

Direct air capture — giant air-filtering machines get the job done for $600–$1,000 a ton. The problem is dilution. CO₂ is 0.04% of the air, so to collect one ton you have to comb through the carbon scattered across roughly 1.3 million cubic meters of atmosphere — a cube of air about 110 meters on a side, taller than a 30-story building — and then heat a sorbent to shake the CO₂ back off. The theoretical thermodynamic floor is about 240 kWh a ton, but real machines burn ten times that or more, because they have to run fans and supply heat. Here the energy bill is the floor, and it’s why the aspirational target is still $400–$600, not $40.

Cement and chemicals — about $60–$100 a ton for cement, ~$110 and up for chemicals. The mechanism is not so different than in DAC, but here the CO₂ comes concentrated from an industrial process. Around 60% of cement’s emissions aren’t from fuel at all; they’re chemistry, CO₂ driven straight out of the limestone as it’s cooked, and no amount of clean energy touches that. But the gas leaves the kiln as a thick stream, 20–30% CO₂ instead of 0.04%, so scrubbing it out costs roughly ten times less than pulling it from open air. Ammonia plants are cheaper still, because they already vent a nearly pure CO₂ stream you can simply catch.

Green steel — roughly $200 a ton, north of $500 where power is expensive. Making steel without coal means making it with hydrogen, and making hydrogen means electricity — about 2.6 MWh per ton of steel, plus another to run the furnace, call it 3.5 MWh a ton. Put that against the world’s ~1.9 billion tons of steel a year and you need more electricity than the entire United States generates — about half again as much — built from scratch and all of it clean. Green steel isn’t really a metallurgy problem, it’s an energy problem.

Ocean electrochemistry — $100 to $800 a ton. Run a current through seawater and you can split it into an acid and a base; dose the base back into the sea and it drinks up CO₂ like a planet-sized antacid. It works. Companies like Equatic are selling it around $500 and chasing under $100 by 2030. But the current is the catch: even on optimistic numbers it takes on the order of 1.4 MWh per ton, so a gigaton-a-year industry would swallow roughly a third of all US electricity. Again, cheap, clean power is the whole ball game.

Ocean shipping — $130 to $1,000 a ton. Green ammonia and methanol are really just hydrogen wearing a more shippable coat, so they inherit the electricity bill; the top of the range ($700–$1,000) is the genuinely clean stuff. Ships need dense, storable energy, and clean dense energy costs more to make.

Aviation’s e-kerosene — $2,000+ a ton, the most expensive thing here. This is where the costs pile on top of one another. To make synthetic jet fuel you need carbon (captured from the air — so you inherit direct air capture’s whole bill) and hydrogen (electricity, again), and then you spend still more energy welding them into a fuel molecule, shedding most of it as waste heat at every step. Feed in 100 units of clean electricity and about 40 come out the far end as fuel. You’re running DAC and then paying a second and third time to turn its output back into something you can burn. It works, if you can call something that’s an order of magnitude more expensive than everything else “working.”

Enhanced weathering — $80–$200 a ton. Certain rocks pull CO₂ from the air as they weather; crush them fine and spread them on fields or beaches and you speed up a key natural process. The floor here isn’t energy, it’s sheer tonnage. You need something like 1.2 tons of rock per ton of CO₂, so a gigaton-scale industry means mining, grinding, hauling and scattering about 1.2 billion tons of rock every year. Picture the biggest mining trucks on Earth, the 360-ton haulers, each loaded with its share: bumper to bumper that line would run about 50,000 km — long enough to circle the equator and keep going a quarter of the way round again. Moving stuff at that scale is never cheap.

BECCS — $50–$200 a ton. Grow plants, burn them for power, capture the CO₂, bury it. The plants do the capture for free, on sunlight — but sunlight is diffuse and photosynthesis banks only about 1% of it, so the binding constraint is land. Pulling down a gigaton a year this way would take roughly 30 million hectares planted in nothing but fuel — about the area of Italy, replanted every year. Scale it to the levels the climate models lean on and you’re eyeing a serious slice of the world’s cropland. Land is the floor, so now carbon dioxide removal is in direct competition with food production and wildlife.

Biochar — $125–$200 a ton. Char biomass instead of letting it rot and the carbon stays locked up for centuries, while the pyrolysis throws off usable heat as a bonus. It’s the cheapest engineered removal going, which is why it’s roughly 90% of the durable removal actually delivered so far. Its floor is the feedstock. That can be cheap if you’re burning waste — sawmill offcuts, crop residue, nutshells. Run out of waste and you’re back to growing biomass on purpose, at which point biochar inherits BECCS’s land problem.

Kelp — thousands of dollars a ton, median around $6,400. Growing seaweed and sinking it sounds like it ought to be nearly free; the ocean grows the kelp. But everything around the kelp is costly: seeded twine, moorings, vessels, labor, storms, and the befuddling, awkward problem of proving the carbon actually stayed down. You’re running an offshore farm to raise a crop whose only value is its carbon, then financing a complicated science project to verify it worked. Ocean operations set the floor, and the open ocean is an expensive place to work.

Trees — $5–$50 a ton, but they don’t really count. What kind of monster could be against planting a tree!? Photosynthesis is free, which is why it’s the lowest number on this list. If you tried to scale it, you’d run into the same land availability limits as BECCS and biochar, but that’s not the real problem. The real problem is permanence — fire, drought, rot, or a chainsaw can hand the carbon back within a few decades. This is a list of durable removals, trees don’t count.

Phytoplankton — $5–$15 a ton. This is the one I work on, and it’s cheap for the same reason trees are cheap: photosynthesis. In the sunlit ocean, microscopic ocean plants already fix staggering amounts of carbon for free; across huge stretches of sea the only thing capping that growth is missing nutrients. Where only iron is missing, a single atom of iron can lead to the removal of 23,000 molecules of CO₂. We’re talking pennies’ worth of material per ton of CO2 removed. Where phosphates or other stuff are in short supply, material costs are higher but still very manageable, maybe $5 per ton. Sunlight provides the energy, and gravity the permanent removal. You’ll never run out of room to do this in — up to half the surface of the planet is covered in marine deserts where these approaches could work. Deployment would cost something, though since you’re mostly adding mineral nutrients to the surface you could easily do this with unmaned surface vehicles. What really drives costs is measurement — proving how much carbon sank and proving that it stayed sunk.

Phytoplankton carbon removal isn’t proven yet — we’re working on it! But if we thought about this problem logically, we would focus the bulk of our research energy here because it has a much, much lower cost floor than other proposed approaches.

The real payoff comes from the mindset shift. Come at CDR with an engineering mindset and you end up trying to capture carbon by out-muscling physics with giant machines. Phytoplankton isn’t like that. It’s a nature-based solution: you’re not inventing a new carbon dioxide removal mechanism, you’re piggybacking on the oldest of all the carbon dioxide removal mechanisms, the one evolution came up with billions of years ago.

That’s the bet. And yes, I am fundraising: if you have a couple of spare million dollars lying around and want to help make it happen, you know where to find me.

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If you’re serious about climate science, the thing that keeps you up at night is the tipping points. We know we’re now flirting with irreversible state-changes in the atmosphere that could yield sharply different climate patterns. The “what” is relatively clear here. The “when” is a lot murkier.

Before we go any farther, I want to be explicit, because there’s always some jerk in comments to get this wrong: the point here is not that “we don’t know anything about climate change.” We know a lot. On some things, we even have certainty. When it comes to extreme heat, for example, it’s “virtually certain” — >99% likely — that hot extremes, including heat waves, have become more frequent and more intense across most land regions since the 1950s, and IPCC attributes this with high confidence mainly to human-caused warming (IPCC AR6 WG1, Ch. 11).The IPCC can say that because different teams using different methods have consistently converged on a similar answer.

That kind of convergence is thin on the ground in the discussion about tipping points, and thinner still when it comes to tipping point timing.

A tipping point is a threshold. Push a system past it and it flips to a different state. The theme here is irreversibility: once you’re past the tipping point, it’s too late to go back. Nudge a chair past its balance point and it crashes to the floor. Standing the chair back up — assuming it hasn’t shattered on impact — will take far more resources than keeping it upright in the first place.

The tricky bit is that the crossing of the threshold and the actual harm often work on completely different clocks.

Scientists call the first the commitment (the moment you’ve crossed the line) and the second the realization (when the pain hits).

For a tipping chair, the lag from commitment to realization is counted in milliseconds; for an ice sheet, it could be a thousand years.

When a screaming headline or a grim tweet gives you a single date for a tipping point, it’s almost always collapsing these two very different things into one date. That impoverishes the debate, because it’s the time lag between commitment and realization that makes tipping points such a hairy problem.

Different tipping points are different. So much so that lumping them together as “tipping points” is itself a little misleading. Still, I want to look at the two most often talked about — the loss of the West Antarctic Ice Sheet, and the collapse of the Atlantic Meridional Overturning Circulation, not because they’re necessarily the most damaging, but because they’re the most intensively researched and best understood. My goal is to try to get some handle on the “when” question. I think if more of us had a clear grasp on how uncertain the answers are, we’d have a more nuanced climate debate.

1: The Doom of the West Antarctic Ice Sheet

There’s a mass of ice in Antarctica sitting on bedrock that mostly lies below sea level, on a bed that slopes downward as you go inland. Once the ocean gets under the edge and the grounding line (where ice lifts off its bed and starts to float) begins retreating downhill, it can keep retreating on its own — a runaway called marine ice-sheet instability. West Antarctica holds enough ice to raise global sea level by roughly 3 to 5 meters.

That’s the headline, but as always in Earth System science, when you zoom in you discover an unholy mess of conflicting claims, theories and observations. There are, in fact, two proposed ice sheet collapse mechanisms, and they give rise to very different forecasts on quite different timelines.

The tamer one is the marine ice-sheet instability just described. The more explosive one is marine ice-cliff instability: the idea that once you expose a tall enough ice cliff at the ocean’s edge, the cliff simply can’t hold its own weight and collapses, exposing a new cliff behind it, which collapses in turn, in a chain reaction that ends with you underwater.

In 2016, DeConto and Pollard built ice-cliff collapse into a model and got an alarming result: Antarctica alone could add more than 1 meter of sea-level rise by 2100 (DeConto & Pollard 2016, Nature). Yes, this is a number derived from the old, mostly debunked RCP8.5 scenario, but given that climate sensitivity seems to be higher than most researchers thought, that in itself doesn’t mean it’s invalid.

Then in 2019, Edwards and colleagues re-examined the question. Rebuilding the analysis with the mechanism included but properly calibrated, they got a most-likely Antarctic contribution of about 45 centimeters by 2100—less than half of the previous estimate. When leaving the mechanism out entirely, the most-likely contribution dropped to just 15 centimeters (Edwards et al. 2019, Nature).

So West Antarctica’s contribution to sea level this century runs from six inches to over three feet, and which number you believe depends largely on whether you think ice cliffs shatter — a question the field has not settled.

But when is the commitment point? Here the news is bad. Some of the field thinks parts of West Antarctica are already past the point of no return. The Amundsen Sea sector — the Thwaites and Pine Island glaciers, the ones you may have seen called the “Doomsday Glacier” — sits at the low end of every threshold estimate. A 2025 modeling study spanning the last 800,000 years found that collapse can be triggered by ocean warming of just 0 to 0.25 °C above today’s temperatures — that is, at or essentially at current conditions (Chandler et al. 2025, Communications Earth & Environment).

Kaitlin Naughten of the British Antarctic Survey, lead author of a 2023 study on Amundsen Sea ice-shelf melt, put it bluntly: “It looks like we’ve lost control of melting of the West Antarctic Ice Sheet. If we wanted to preserve it in its historical state, we would have needed action on climate change decades ago.”

Her study found that faster ocean-driven melting this century is now essentially committed regardless of emissions — there was no meaningful difference between a middle-of-the-road scenario and the most ambitious Paris target (Naughten et al. 2023, Nature Climate Change).

But Naughten was talking about melting on this century’s timescale — not the multi-meter sea-level disaster movie outcome, which is a much slower and separate story.

Because for sea-level rise itself, the timeline is distressingly wobbly.

DeConto and Pollard’s 2016 model, with the ice-cliff mechanism switched on, gave more than a meter by 2100 and more than 15 meters by 2500 under RCP8.5. Edwards and co., with the same mechanism switched off, cut the 2100 figure to about 45 centimeters. The 2019 expert elicitation led by Bamber put the median contribution to sea levels from both ice sheets (Antarctica and Greenland) combined at roughly 26 centimeters by 2100 in a 2 °C world, with about a one-in-twenty chance (at the 95th percentile) of exceeding 2 meters of total sea-level rise under high emissions.

A 16-model ensemble published by Seroussi in 2024 projected that Antarctica’s contribution to sea-level rise would remain under 30 centimeters by 2100, but would then accelerate violently, spiking to as much as 4.4 meters by the year 2300. Golledge’s 2015 modeling gave a similar shape: a mere 0.01 to 0.38 meters by 2100, but 0.2 meters to more than 5 meters by 2500. And Joughin’s 2014 study of Thwaites concluded that a collapse of that one basin was “likely within the next 200 to 1,000 years.”

So for the year 2100, the estimates span from a few centimeters to more than a meter — a more-than-tenfold spread. For the ultimate multi-meter rise, the estimates span from the next couple of centuries to the next several millennia. The basic story — a near-term trigger with a slow, centuries-long climb to ultimate horridness — is more or less agreed on. On the actual dates, the field is all over the map.

2: AMOC Amuck

The Atlantic Meridional Overturning Circulation — the system of ocean currents that carries warm surface water north (the Gulf Stream is one part of it) and cold water back south at depth. It’s a big reason Bordeaux does not have the winters Montreal has, even though they sit at pretty much the same latitude. Freshen the North Atlantic with enough meltwater and the supply of warmth to Europe can weaken and, in principle, just stop.

When it comes to conflating the commitment date and the realization, AMOC coverage is systematically among the worst offenders. But the tipping point is one event, the circulation actually winding down is another, and the cold-winters, failing-farms, rising-seas impacts are a third. The public argument has been almost entirely about the first of these events. Science has not yet pinned down any of the three.

In 2023, Peter and Susanne Ditlevsen fit a statistical model to a century and a half of ocean-temperature data, extrapolated the loss of stability, and produced an actual calendar year. Their headline number: A central collapse estimate of 2057, with a 95% confidence range of 2025 to 2095 (Ditlevsen & Ditlevsen 2023, Nature Communications).

That’s a shockingly near-term, shockingly specific claim — the threshold possibly crossed within a decade or two, most likely mid-century. It got enormous attention. But read it precisely: it is a commitment date, not an impact date. Even if the Ditlevsens are exactly right, 2057 is the year the system is doomed, not the year Europe freezes.

Backing up the “sooner than we thought” direction, van Westen and colleagues in 2024 produced the first simulation of an AMOC tipping point in a full-complexity climate model and concluded the real-world AMOC is “en route to tipping” (van Westen et al. 2024, Science Advances). And Stefan Rahmstorf of the Potsdam Institute, reacting to the Ditlevsen paper, wrote, “the scientific evidence now is that we can’t even rule out crossing a tipping point already in the next decade or two.”

Does everyone agree? Of course not.

Baker and colleagues analyzed 34 climate models under extreme greenhouse-gas and meltwater forcing and identified a stabilizing mechanism (winds pulling water up in the Southern Ocean) that the more alarming studies leave out. Their conclusion: a full collapse this century is unlikely — AMOC weakens a lot, but doesn’t shut down (Baker et al. 2025, Nature). Bonan and colleagues, using observations to constrain the models, found only “limited” weakening of about 18–43% by 2100, and no collapse. And the IPCC’s assessed position is “medium confidence that the AMOC will not abruptly collapse before 2100” (IPCC AR6 WG1).

So on question one alone — the commitment date — the field spans from “possibly within a decade or two” to “not this century.”

But suppose the threshold is crossed. The collapse doesn’t happen the next morning; it plays out over some stretch of years, and only then do the impacts fully land. And this second lag is a range so wide it makes the precision of the debate on commitment date look faintly ridiculous.

The big tipping-point synthesis puts the collapse timescale at a central estimate of about 50 years, with a range of 15 to 300 years (Armstrong McKay et al. 2022, Science).

Van Westen’s simulation had the collapse, once begun, completing in under 100 years — “a slow decline can lead to a sudden collapse,” in their phrase — with parts of northwest Europe then cooling by more than 3 °C per decade, a rate of change with no modern precedent (van Westen et al. 2024). This is proper disaster movie stuff, and yes, it’s entirely within the realm of possibility.

But the most vivid impact figures you may have seen (London winters hitting −19 °C, Edinburgh −30 °C, up to a meter of North Atlantic sea-level rise) come from a follow-up that explicitly describes a far-future equilibrium state, not the coming decades (van Westen & Baatsen 2025, GRL). How far-future is far-future? The researchers never say, just “several hundred years from now.”

This refusing-to-hazard-a-guess thing is instructive. On the timing question, some of the most careful researchers concede the uncertainty is so wide, they refuse to play the calendar game. Niklas Boers, whose 2021 study is one of the foundational AMOC early-warning papers, deliberately gave no date, saying plainly “the AMOC’s stability has declined. It has moved closer towards a possible tipping point. But we cannot say when that might happen.”

And as René van Westen, lead author of the “on tipping course” study that alarmed everyone, puts it, “we are never going to get a [fully] reliable ‘early warning’ because the uncertainties around the data availability are just too large.”

Then there’s one study that hasn’t made much noise. In 2024, Maya Ben-Yami, Niklas Boers, and colleagues took the same category of method behind the “2057” forecast and stress-tested it: they ran it on different datasets and with different reasonable analytical choices to see how stable the predicted tipping date was.

The predicted AMOC tipping times ranged from 2050 to the year 8065.

So, a six-thousand-year window (Ben-Yami et al. 2024, Science Advances; TUM summary). Lead author Ben-Yami says, “our research is both a wake-up call and a cautionary tale. There are things we still can’t predict... The stakes are too high to rely on shaky predictions.”

When your method can put the answer anywhere between the lifetime of a person born today and the fall of a civilization not yet founded, that’s just a polite way of saying “we have no idea.”

Look, this post looks briefly at two hypothesized tipping points. There are lots more in the literature. There are probably still more in nature that we haven’t identified at all. And many of them share the traits that decision theorists describe as giving rise to deep uncertainty.

Deep uncertainty attaches to problem where the experts don’t just disagree about the odds — they can’t even agree on the underlying mechanisms, on what counts as proper data, on the probabilities, or in some cases on which outcomes are on the table in the first place.

Climate tipping-point timing is deeply uncertain. The mechanisms are disputed, and different mechanisms give rise to different timelines. The observations are too short and too indirect — we’ve only measured the AMOC directly since 2004, so the long-term claims lean on proxies that at least some people in the field find iffy. The models disagree with each other. They all have serious blind spots — the simpler models produce collapses the complex ones don’t, and the complex ones are suspected of being systematically too stable.

We are steering a system with long lags, irreversible thresholds, and no (or a very faulty) speedometer. The people who study it most closely keep squirming when we try to pin them down on a date. This happens not because scientists are incompetent, but because they are scrupulously reporting on very sophisticated attempts to forecast insanely complex processes that actively resist being forecast.

Deep uncertainty creates a rich environment for confirmation bias. Whatever your political priors are going into this debate, you can find a study to back them. If you’re a catastrophist and you think AMOC is going to sputter to a halt next year, you can find a study to back that. If you’re a denialist and think AMOC’s good for the next 8000 years, you can find a study to back that. You pays your money and you takes your choice.

No wonder public debate is so unsettled: when the science is in this sort of state, if you “follow the science” you can end up pretty much anywhere.

The question, really, is how we’re supposed to make decisions under uncertainty as deep as all this. I’m increasingly obsessed with this question, because I’ve yet to find anyone able to offer up a really satisfying conclusion.

I’m developing a view about it, which definitely needs some stress-testing, but dwells on the things we would want to do regardless of whether we turn out to be on an apocalyptic path, or merely an annoying one. The category decision theorists lump these sorts of low-regret policy paths under is “robustness”. It will come as no surprise to people who read this substack that I think the most robust way forward leans hard on low-cost carbon dioxide removal, and phytoplankton is the only way to do that — but this post is already too long, so I’ll develop that theme in another post.

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Here’s a climate thought experiment.

The year is 1526, and you’re the monarch of some great power. An angel appears and tells you that if you make a painful sacrifice on behalf of your kingdom —say, extracting 20% more in taxes from your already dirt poor subjects — you will be able to prevent some catastrophic evil 500 years in the future. An apocalyptic outbreak of plague, say, forecast for the first half of the 21st century.

You know that, a couple of centuries prior, something like a quarter of the people of Europe died from the plague. So you have every reason to believe this threatened harm would be catastrophic.

Should you make this sacrifice, squeezing the peasants you rule on behalf of the people of the far future?

There are good reasons to think you shouldn’t, even if you believe every word the angel says.

You could say, with some verisimilitude, that the subjects of the far future are not really your responsibility. You could conjecture —correctly, as it turns out— that they’re likely to be far wealthier than the medieval peasants you reign over. You could guess —also correctly— that by the beginning of the 21st century, they will have invented a cure for bubonic plague, making a big sacrifice futile.

Knowing what we know today, I think we can say unambiguously that a 16th century monarch would have been wrong to sacrifice prosperity in his time for such an uncertain benefit so deep in the future.

Shouldn’t some awareness of this dynamic color the way we think about responses to climate catastrophes that, as far as we can tell, may be both very real and potentially quite distant in time?

What if, in relation to the people of the 26th century, we in the 21st are the medieval peasants, ignorant of our own relative poverty and backwardness, scared of threats that won’t look so threatening to the people of the deep future?

I find myself mulling thought experiments like this one now and then, as I think about how we should respond to threatened climate catastrophes. Not because I don’t think climate hazards are real — they’re very real. And not because I think we should do nothing to counter them — I spend my entire working life thinking about what we should do to counter them.

Instead, I dwell on them because I find it frustrating that the element of time is so often elided in questions about existential climate threats.

Because it is absolutely true that we’re flirting with climate tipping points that, were they to play out across a single generation or two, would be absolutely catastrophic.

It’s super easy to scare people telling them AMOC is about to collapse and that will ultimately mean European winters ten degrees colder than what we’ve known.

It’s easy to scare people telling them the West Antarctic Ice Sheet may already be past its tipping point and will ultimately mean sea levels rising as much as 10 meters from where they are now. If you leave out the time dimension, people naturally tend to imagine the full impact happening next year and obviously that’s a catastrophe.

In reality, the damage we would face for setting off these tipping points turns entirely on how long an adaptation period we’ll have. If European winters get, on average, two degrees colder per century over the next five centuries, Europe will adapt. Yes, the Londoners of 2526 will have to deal with the winters Newfoundland has in the 21st century, but then no Londoner in 2526 will have any memory of the old days, and the city will adapt. It will, by almost any reckoning, be a much more affluent London than that of today, and may very well innovate ways of dealing with colder winters as alien to us as the idea of antibiotics were to the monarchs of the 16th century. And sea levels that rise 6 m. per decade are an entirely different type of calamity than they would be at 60 cm. per decade. One puts civilization under enormous strain, the other one mostly just annoys us.

There’s a certain tendency, in catastrophist/accelerationists spaces, to act as though the possibility of catastrophic outcomes in the future were the beginning and the end of the debate about climate change.

People talk about the potential cataclysm that would follow from the thawing of Siberian permafrost as though it was enough to sustain any amount of current spending for prevention. If some potential outcomes carry an essentially infinite cost, this line of argument goes, then the expected value of seeing them come to pass is infinite no matter how small the probability chance we assign to them.

The thinking, transposed to 1526, comes out as “well, we just saw bubonic plague kill half the people alive, no sacrifice is too big to prevent it happening again.”

I think we need to resist this form of thinking. It’s plainly wrong. Worse, it’s unhelpful.

In the real world, decision-makers have no choice to trade off between incommensurable priorities. Children still need educating, roads paving, hospitals staffing and armies still need arming, however hazardous climate hazards may be. If your hazard function contains no limiting principle, if it doesn’t generate a basis for accepting some mitigation efforts but rejecting others, it can’t serve as a guide to action.

Where climate hazards are unlimited, but their timelines are unknown, models are always going to be an uncertain guide to action. The cold, hard reality is that whether we end up spending too much or too little to manage them will only be known ex post.

From today’s vantage point, all we can say for certain is that we ought not to waste the resources we do devote to managing climate hazards. Given the unquestionable political reality that willingness to spend is limited, and hazard exposure is not, the one thing we cannot abide is waste. If you take climate hazards seriously as hazards, then every climate dollar should be ruthlessly scrutinized for how much warming it prevents.

Here, I think we can say unambiguously that our performance has been atrocious. With climate fully subsumed into the nonsense back-and-forth of partisan polarization, the vast bulk of what passes for climate activism is blissfully disconnected from any recognizable version of atmospheric physics. We pour money into symbolically resonant projects in the absence of even a rudimentary cost-benefit analysis, as though the intention to make a difference mattered more than the actual impact achieved.

The preening, virtue-signalling brand of climate politics is exactly as fallow as the callous, vice-signalling antics of the denialist right. That’s not surprising, of course: climate realities are convoluted and confusing, partisan signalling is simple and feels good.

Still, somebody has to be the grown up in this room. Somebody has to point out that our resources remain limited, even if our hazard exposure isn’t, and that being the case, we certainly can’t afford to waste what resources we can devote to this problem. I get it that that’s not a message that will sustain a mass movement, I know it won’t fit on a bumper sticker. But it’s true, damnit, and that ought to count for something.

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I spent the first half of last year trying to find the answer to a single question: how can we remove carbon dioxide from the atmosphere at a scale that will actually move the climate needle?

Like many before me, I had come to the conclusion that there was no realistic path to emissions reductions quick enough to sidestep some pretty scary climate risks. I had also come to think that the most usually discussed alternative approach —solar geoengineering— is probably never going to be socially or politically acceptable. So large scale carbon dioxide removal (CDR) was going to have to be it.

But how?

Most approaches you read about in the CDR space seem totally unworkable at scale. Most are far too expensive, others keep carbon out of the atmosphere for just 20-30 years, others make extravagant demands on land or industrial production. I crossed them off my list one at a time.

In the end, I was left with just one item: a variant of ocean fertilization that tries to stimulate phytoplankton growth in warm, subtropical oceans that don’t have enough fixed nitrogen.

Now most people have just never heard of ocean fertilization. When I bring it up, mostly I get blank stares. Among the tiny sliver of the truly climate-obsessed who do know what I’m talking about, usually people have only heard of the cold-water Ocean Iron Fertilization proposals that were briefly popular 20 years ago.

Nitrogen-fixation-based phytoplankton carbon is a niche within a niche within a niche. But the more I learn about it, the more I think NFix may be the answer to the question I started with.

This one takes a bit of explaining, so I’m going to go long.

Out of Redfield

The story starts about 100 years ago, when early ocean scientists began to realize that marine life is extremely unevenly distributed across the ocean. There’s lots of life in oceans near land, but the farther out you get into the open ocean, the fewer living things you find. Get very far from a continent, towards the center of the big rotating ocean currents known as gyres, and you find yourself in a series of marine deserts: vast areas of the ocean that host almost no life.

The reasons for this weren’t really mysterious. All marine food chains begin with the microscopic plant-like organisms known as phytoplankton that first turn sunlight into food. Like all living things, phytoplankton need certain nutrients to thrive. Chief among them are two macro-nutrients: bio-available nitrogen and phosphorus.

In warm waters far from land, those nutrients just weren’t very common in the sunlit upper layer of water, so it was not surprising there wasn’t much phytoplankton. And since everything in the ocean either eats phytoplankton or something that ate phytoplankton, the absence of the nutrients they need was enough to explain why there was so little life in general.

Scientifically, the fact that the center of the ocean didn’t host much life wasn’t particularly noteworthy. The scientific puzzle was elsewhere: farther North and South some cold water oceans seemed to have plenty of nutrients. Fixed nitrogen and phosphorus was plentiful in the water, and so were micronutrients like iron and zinc, but there was very little phytoplankton, and very little life.

That didn’t seem to make sense: normally big piles of food don’t just sit there uneaten — something evolves to take advantage of untapped resources.

What became known as the High-Nutrient, Low-Chlorophyll (HNLC) anomaly became a kind of obsession for oceanographers: every time they tested the waters, they’d find a full complement of nutrients, and almost nothing eating them.

Why?

The story of how the HNLC anomaly was solved became the stuff of oceanographic legend. In the 1980s, a single, charismatic oceanographer by the name of John Martin came up with an ingenious thesis and set out to prove it. The waters in HNLC regions, Martin argued, were missing one key nutrient — it’s just that that nutrient happened to be the thing that oceanographic vessels are made of.

Because steel is mostly iron.

Martin’s insight was that oceanographers had been contaminating their own samples for fifty years, because the ships they sailed on inevitably release trace quantities of iron into the waters they were sampling. To avoid this, he designed a famously exacting new protocol to sample HNLC waters on rubber dinghies that contained no iron at all, and proved that what these waters were missing was indeed iron.

This caused quite a lot of excitement in oceanography — but I’d argue it also set the profession down the wrong track.

For the next 30 years, oceanographers became obsessed with the iron hypothesis. They commissioned more than a dozen expeditions to go to these remote areas of cold water and see what would happen if you added iron to the surface. And they found that, darn it, John Martin was right — tiny iron additions led to huge spikes in phytoplankton — HNLC regions turned out to be high in macro-nutrients, but critically lacking in a single, critical micro-nutrient: iron.

The profession’s single-minded obsession with the HNLC regions was scientifically justified. But it meant that relatively little thought went into developing the carbon capture potential of those less scientifically interesting warm oceans. Instead, the field became infatuated with the idea that you could fix climate change by adding iron to low-productivity cold HNLC waters.

Some serious researchers still think this could work. By and large, though, I’ve found most oceanographers are skeptical, because of two problems that have always hounded Ocean Iron Fertilization in HNLC waters .

The first is the durability of sequestration.

It’s easy to get a massive phytoplankton bloom by sprinkling iron into an HNLC region. What happens next is that those tiny plants get eaten by tiny animals, zooplankton. And when the zooplankton digest them, the carbon dioxide that was in the phytoplankton gets expelled right back out into the surface water, from which it soon rejoins the atmosphere. This is called remineralization, and it’s the original Achilles’ heel of ocean fertilization.

So that’s pretty concerning, but it’s not the only reason so many oceanographers are skeptical.

From the earliest days of the Iron Hypothesis, oceanographers have also worried about nutrient robbing: the idea that, in nutrient terms, iron fertilization is just robbing Peter to pay Paul.

Even if you can spark a big bloom, and even if that big bloom does capture carbon dioxide for the long term, that bloom will inevitably take up the macro-nutrients in the water — depleting the fixed nitrogen and phosphate that made the HNLC region HN in the first place. When that water mass circulates to areas of higher productivity — near a coast, say, or an upwelling zone— it will be less able to sustain phytoplankton, because its nitrates and phosphates will have been used up.

In this view, all iron fertilization does is change when and where phytoplankton develops, not how much. In some sophisticated versions of this argument, nutrient robbing could turn fertilization into a net ecological negative, with potentially serious impacts on downstream fisheries.

There are other, more niche concerns too about deoxygenation and nitrous oxide production. But remineralization and nutrient robbing are the concerns that oceanographers bring up every single time.

Look closely, and you see these are not objections to ocean fertilization in general.

They’re objections to one specific approach: cold water Ocean Iron Fertilization in HNLC regions.

The vast bulk of the world’s marine deserts, however, are not in high-nutrient, low-chlorophyl parts of the ocean. Most marine deserts they’re in warm sub-tropical ocean gyres, which are classic low-nutrient, low-chlorophyl (LNLC) waters.

Ocean fertilization, but not as you know it

Way back in the 1980s, a tiny band of contrarian oceanographers started arguing that HNLC might not be the best target for fertilization. Centered around a handful of researchers at the University of Southern California, they began to build the theoretical foundations for an alternative approach, one that promised to sidestep remineralization and nutrient robbing issues by centering on an entirely different approach, in an entirely different kind of ocean regime.

Granted, at first sight, trying to make low-nutrient oceans fertile seems like a terrible idea. Unlike HNLC regions that just need miniscule, trace quantities of iron to sustain photosynthesis, LNLC regions are missing macro-nutrients: the major building blocks of life. They often have almost no nitrates and are low on phosphates too, and here we’re not talking about trace quantities, we’re talking about massive amounts of complex molecules. This sparks nightmare visions of large chemical fertilizer plants burning natural gas to run Haber-Bosch nitrogen fixation. The logistics of that are daunting, and the economics beyond hopeless.

Except, there’s another way.

Gardners have known for years that you don’t necessarily need a chemical plant to fix nitrogen, you can also do it with a bean stalk. Beans host microbes around their roots that have evolved to catch inert atmospheric nitrogen (N₂), break up its triple bond, and fix it into the kind of fertilizers plants need to grow. Turns out there are bugs in the ocean that do the same thing. A key paper in opening this discussion was this 1982 beaut by Doug Capone discussing trichodesmium, an ocean microbe that runs the same biochemical pathway and fixes nitrogen in the water exactly the same way the bugs that live on beanstalk roots do on land.

This whole thing about nitrogen-fixing microorganisms seemed of, at best, academic interest until scientists identified this process operating in nature.

The breakthrough came courtesy of research into hydrothermal vents. In the South Pacific, off the coast of Tonga, you find these undersea volcanoes that are actually quite shallow. Shallow enough that the plume of minerals they put into the water reaches the sunlit layer of the ocean, the bit where phytoplankton grow.

The darn things are running a picture perfect natural experiment on what a warm water fertilization program might do.

The vents demonstrate that adding nutrients to the upper ocean does exactly what you would wish: it captures an enormous amount of carbon dioxide. How? By turning Low-Nutrient waters into High-Nutrient waters. And how do they do that? By feeding the bugs that capture N₂ from the air and fix it into bio-available form.

It’s an incredibly cool finding, and one with major implications for iron fertilization in LNLC regions. Because —and this is the message that even most Oceanographers seem not to have quite grasped yet— LNLC fertilization addresses both of the major criticisms against HNLC fertilization.

Remember, HNLC fertilization gets slammed for nutrient robbing: the idea that fertilized patches just soak up the pre-existing stock of macronutrients, depriving downcurrent communities of those nutrients. But Nitrogen Fixation based approaches certainly don’t do that: NFix adds new macronutrients to the ocean.

The newly fixed nitrogen that’s driving phytoplankton growth around these vents sites isn’t being stolen from downstream communities, it’s been newly fixed straight from the air. And while you can’t fix phosphate from thin air the way you can fix nitrogen, many lines of research suggest phytoplankton can stretch their phosphate budgets much farther than they can stretch their nitrogen. In other words, if there’s not enough fixed nitrogen, phytoplankton just don’t reproduce. But where there’s not enough phosphate, in many cases they adapt and keep growing. (There are limits to how far they can stretch a limited phosphate budget, of course, but those limits are a lot less stringent than for nitrogen.)

Then there’s remineralization: in cold HNLC waters, when the phytoplankton gets eaten, the whole system just stops and the CO₂ goes right back out to the air where it started. When you add fixed nitrogen, though, the picture changes: when a zooplankton eats a phytoplankton, it’s not just the CO₂ that gets remineralized, it’s also the fixed nitrogen! That ends up right back in the water, where it drives a whole new cycle of phytoplankton fertilization. Oceanographers call this regeneration, and to them, it makes perfect sense. In a nitrogen-limited system, which is what LNLC waters are, the organisms in the water are desperately hungry for fixed nitrogen. This is what makes LNLC different from HNLC: in HNLC systems, pools of fixed-nitrogen just sit there, unused, on the ocean surface for lack of iron.

In LNLC systems, any fixed nitrogen that hits the water is quickly consumed to regenerate phytoplankton. In this kind of ocean regime, remineralization is unlikely to end up re-emitting CO₂ to the atmosphere. Instead, it just becomes part of the regeneration cycle.

And there are other subtler reasons to think LNLC oceans may do better at long-term carbon storage than HNLC regions. The warm waters where LNLC conditions develop are thermally stratified: a relatively warm layer sits on top of the water column. As it’s less dense, it acts as a lid on the system, preventing deep mixing. This tends to counter the tendency of carbon that has been captured from rising back up to contact with the atmosphere. Less deep mixing also means the surface waters have more time to equilibrate their CO₂ content with the atmosphere, which theoretically ought to improve sequestration efficiency.

Still early days

If you’ve read this far, congratulations! You now have a better grasp of next generation ocean fertilization techniques than most oceanographers.

Does this mean that Nitrogen-Fixation based fertilization will definitely work as a carbon capture pathway?

Hell no!

We have years of scientific research to do before we can design a workable deployment protocol. There are definitely risks — it may be that we run out of phosphates faster than we expect, it may be that we deoxygenate the water column more quickly than we realize, it may even be that we select for harmful algal blooms, or increase the production of Nitrous Oxide in the ocean.

There’s quite a lot of careful work still to be done before we can really say NFix will work at scale, and we’re not taking anything for granted.

What I can say from direct experience is that every scientist working in this field is very well aware of the risks, and committed to researching this pathway responsibly. People outside the field sometimes get the sense that the people who are into fertilization are a bunch of cowboys, in my experience, it’s more like a small group of very sane professional oceanographers who’ve spent their entire careers studying the ocean and are very aware of how precious these ecosystems are.

They’re also very attuned to the risks of runaway climate change, though, and understand that it makes no sense to obsess about one set of risks while ignoring the other.

I’m excited about these new fertilization approaches because it seems like it could work and I think if we do it carefully, we can do it safely — but I know that’s a far cry from proving that it will work and it is safe.

Still, the takeaway here is that the vague sense in the climate world that Ocean Fertilization is off the table needs to be revised. That view developed around one particular fertilization approach.

Because it’s a big old ocean, and most of it is not cold waters around Antarctica or near Alaska. Most of it —around half the surface of the earth— is sub-tropical waters that don’t have a lot of nutrients and don’t have a lot of phytoplankton.

It may be that a relatively simple, cheap, ecologically benign intervention to rebalance the nutrient profile in those waters can vastly increase the ocean’s ability to absorb carbon dioxide safely. It may be that a simple, low-cost, ecologically benign intervention can stop climate change in its tracks.

Once you see it, it’s hard not to be excited about it.

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There are two ways to stop a bathtub from overflowing: you can stop water from flowing in, or you can allow water to flow out. If your priority is to stop the bathtub from overflowing, the two are equivalent.

The same is true for carbon dioxide in the atmosphere.

For three decades, climate debates have focused on slowing the rate at which we add carbon dioxide to the atmosphere. That approach has mostly failed.

The rate at which we emit carbon dioxide to the atmosphere is still accelerating. In the next 10 years, that rate is expected to start slowing, but not quickly enough to keep global temperatures within internationally agreed targets.

The narrow focus on slowing emissions has tended to obscure the alternative. We can also remove carbon dioxide from the atmosphere. Right now, we don’t have technologies able to do this at the sort of scale that will matter for the climate. Most of the methods people are looking at are either too expensive, too short-lived, or both.

For Carbon Dioxide Removal to make a difference, it needs to be both low-cost and long-lasting. It also needs to be safe for people and the environment.

Only one approach has a realistic shot at meeting all three criteria: marine Carbon Dioxide Removal (or mCDR).

Oceans already soak up about a quarter of all the carbon we put into the air. They hold about 50 times more carbon than the atmosphere does. If we could gently nudge the oceans so they’ll absorb carbon dioxide a bit more quickly, we could solve much or all of the climate problem without bankrupting the world economy.

There are two broad ways of doing coaxing the ocean into absorbing more carbon dioxide: the first involves chemistry, the second biology. I work on biological approaches. The idea is to increase the ocean’s capacity to sustain microscopic marine plants —phytoplankton— that naturally absorb carbon dioxide. I think phytoplankton approaches will win the carbon dioxide removal race because they offer a unique combination of low cost, ecological safety, and scalability.

We’re not there yet. We need a lot more science to learn how to enable phytoplankton growth safely, at scale. My day job is to support the people who are doing that research right now.

mCDR isn’t magical. It works on sound scientific principles that have been around for decades. You don’t hear much about it, because the global climate conversation is stuck in an outdated way of thinking about the problem. And yet it’s the best —and the only realistic— solution to the climate problem. So you’ll be hearing a lot more about it over coming years.

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We’re a meaning-making species, we think in stories. We try to impose some narrative structure on, well, just about everything. We can’t make sense of a thing until we’ve worked out a story about it. It’s just how we’re made.

When we’re faced with the unsettling, strange realization that we, as a species, are changing the earth’s climate, we want it to make sense. Naturally, we tend to interpretations that gel with our broader view of the world. In our hyperpoliticized age, it’s not hard to guess what form this will take. Those who are generally skeptical of capitalism have plenty of raw material to put an anti-capitalist narrative frame on climate change. Those who are more worried about anti-capitalists than capitalism have plenty to work with, too.

The longer I work in climate, the harder I roll my eyes at politicized climate narratives. Catastrophism and denialism seem like variants of the same thing: shoehorning climate into political fights that don’t, in the end, have anything to do with climate. Climate catastrophism is overwhelmingly the domain of watermelon politics — green on the outside, red inside. Denialists deny what they deny from a place of contempt for catastrophists, not from any actual engagement with climate reality. Neither side actually has anything to say about climate as climate. It’s super boring.

The atmosphere doesn’t do narratives. It happily ignores all ideological agendas and follows the only law it knows: thermodynamics. Climate follows its own logic, a physical logic vastly more complex and more interesting than the paper-thin politicized narratives around it.

It’s that logic I want to engage with. The more I do, the more I understand why the politicized narratives ignore it: because it happily baffles both dominant political frames five times before breakfast.

Take the simple, foundational, rock-bottom question: how bad is it? With thousands of climate scientists now working on the problem all around the world and tens of thousands of papers published every single year, you’d think we’d have a basic handle on this question, but we don’t. The data we have pulls in both directions at the same time.

On the one hand, carbon dioxide emissions are just not rising as fast as climate alarmists thought they would even just a couple of decades ago. The demise of RCP8.5 earlier this year made clear the intellectual bankruptcy of some of the shrillest voices on the left. But if you think that’s a reason to relax and settle into the comforting bromides of right-wing climate discourse, the atmosphere has another think coming for you.

Even as emissions settle into a lowish concentration path, global average temperature rise appears to be accelerating. This is something climate models struggle to cope with. James Hansen, the dean of Earth System science, argues that the monster El Niño that’s brewing in the Pacific this year demonstrates those models are just wrong. So now you’re thinking that rescues the left-wing narrative, but that’s wrong too: the acceleration appears to be, perversely, caused by the success of environmental policies to clean up aerosol pollution, which has had the unintended consequence of withdrawing a cooling aerosol shield and letting the earth absorb more solar radiation.

There’s an overpowering urge to read climate news in narrative terms — to cheer the news that bolsters our narrative, boo the news that bolsters theirs. But the atmosphere isn’t going to referee the left-right climate debate: it’s immeasurably more complex than that. Appreciating that complexity demands that we step away from narratives as such and embrace the chaos that the firehose of science is pointing at us.

Much of the problem is that climate sensitivity —the basic question of how much temperatures rise in response to a change in greenhouse gas concentrations— is still a big fat unknown. Think about how messed up that is — the overwhelming reason we’re obsessed with emissions is that we figure lowering them will mean temperatures rise less quickly, but we still don’t really know what temperature rise corresponds with what level of emissions!!

The reason we don’t know is that the relationship is mediated by aerosols and clouds, but the science of aerosols and clouds is in a mess, with mongo error bars reflecting basic confusion about what causes what and how. There is a lot of very sophisticated research going into this problem right now, but those researchers will be the first to tell you they’re not close to solving the problem.

This is why calls to “follow the science” are so unhelpful. “The science” isn’t the tidy answer key in the back of the book that climate activists imagine it to be: it’s a cursed tangle of leads, half developed, pointing in contradictory directions. I have enormous respect for climate scientists, but I also talk to them enough to know they’re more aware than anyone of how far they are from figuring it all out.

The IPCC (the UN’s Intergovernmental Panel on Climate Change) with its mission to synthesize the wild mess of climate science outcomes into a message policy-makers can use, inevitably ends up confusing this issue. I understand the need for some sort of authoritative statement of what it is scientists mostly agree on, and what it is they don’t. But that is much more a function of the needs of policy-makers than of the scientific process. Forcing climate science to speak with one voice risks projecting an illusory consensus. A fully honest IPCC would produce guidance so vague and equivocal that policy-makers would find it worse than useless.

It’s not that climate scientists are incompetent: the ones I talk to are, as a rule, freakishly competent. It’s that the earth system is insanely complex: an overwhelming mess of physical, chemical and biological processes across land, sea and sky all feeding back on one another in non-obvious ways. Earth System scientists have made extraordinarily impressive progress untangling many of these relationships over the last few decades. I’m in awe of these people. Which is why I tend to take it seriously when I hear them say that there are huge gaping chasms around our understanding of the Earth System.

Go into almost any given sub-specialty and you find communities of researchers hyperaware of risks most of us are oblivious about. For my day job, I had to spend a good chunk of the spring looking at the way oceans produce nitrous oxide (N₂O) — laughing gas to you and me, but no laughing matter in climate terms. Nitrous oxide is 273 times more powerful as a greenhouse gas than carbon dioxide, and oceans processes produce an awful lot of it.

Trouble is, the ocean nitrogen cycle is extremely complex, mediated by the still poorly-understood interactions of hundreds of thousands of different species of ocean microbes living hundreds of meters below the surface. As a result, the processes that generate nitrous oxide are in this strange place of being both a subject of intense academic study and an unholy mess of unanswered questions.

Models suggest that increasing ocean stratification, caused by rising sea surface temperatures, may lead oceans to generate quite a lot more N₂O than they have in the past. The processes that do this tend to happen at middle depth, from 200 to 1,000 meters below the surface, which means you can’t get at them with a satellite, you have to go and sample the water, which is impossible to do at any sort of scale. So scientists are having to draw conclusions from pathetically sparse evidence sets, and while the techniques they use are sophisticated there’s only so much that statistical wizardry can do to overcome a skimpy evidentiary basis. All of which means that how much extra N₂O, exactly, oceans may be producing is something we can only roughly guess at. And we know even less about when and where all the added N₂O will ultimately be released into the atmosphere.

Some very cool science is being done to constrain the uncertainty in this area. “Constrain the uncertainty” is a lovely bit of jargon climate scientists use, meaning “to go from knowing fuck-all about a subject to knowing more-than-before (but-still-definitely-not-enough.”) Look, I’m in awe at the people who do this work. But they’re not under any delusion that they’re on top of the problem, because they’re not.

Of course, oceanic N₂O may turn out to be a nothingburger, or it may turn out to be the thing that tips us into an even faster acceleration of mean global temperatures. I’m not trying to make you lose sleep about N₂O specifically (although you definitely should.) N₂O isn’t the point, ultimately: it’s just the one piece of the puzzle I happen to be sensitive to right now, because it’s the one I’ve been reading about.

There are plenty of other areas like this, niche-within-a-niche-within-a-niche bits of climate science that normies have never even heard of: brine rejection and Antarctic bottom water formation, how fast peat bogs in the Congo river basin will release carbon as they warm, how fast frozen subsea sediments around Siberia will thaw. A dozen others I don’t know about. And then there are probably other potential live climate feedback loops that nobody is fretting about just because we’ve not yet identified them.

You often hear people say that climate scientists are especially alarmed by the climate crisis, and that’s true. But people misinterpret that observation. They think it means scientists know something we don’t: that experts have a detailed understanding of the ways we’re fucked that the general public doesn’t have. There’s a comfort in that, a sense that somewhere out there wise people in white lab coats are on top of things, at least on a factual level.

But that’s backwards.

What scientists know that we don’t know is how much they don’t know. That’s why they’re scared.

In the public sphere, climate debates are going to remain trapped along the same old tired left-right axis as everything else. We’re meaning-making animals, we can’t do without our narrative frames. Those frames are orderly, they bring clear good guys and unambiguous bad guys into sharp focus.

The alternative is, in its own way, much scarier. Make the effort to actually look at climate science without overlaying an ideological frame on it, and you find a bewildering mass of often contradictory trends and probabilistic gambles. Uncertainty is absolutely pervasive. And boy is it deep.

That policy is going to get it wrong is pretty much guaranteed: deep uncertainty turns climate policy into Calvinball. You’re playing a game, but you don’t know what the rules are, you don’t know the score, you don’t know who the opponent is, and the rules, the score and the opponent all keep changing.

We’re a meaning-making species; we struggle to cope with situations where meaning is this evanescent. If we want to get it a little bit less wrong, though, we might as well start by doing the hardest damn thing: checking our instinct for narrative frame-making at the door. Putting it on hold, as best we can, long enough to try to actually absorb the exceptionally confusing facts of a problem that really is without precedents in human history.

Very, very few people are able to do this. It’s a very hard cognitive ask. I do my best to try to rise to this standard, and fail several times every day. Scientists struggle with it, policy-makers struggle with it. It’s hard. But if you want to not sound like an arse as you talk about climate, the single best thing you can do is to doubt every single climate narrative. And the more coherent and morally tidy it is, the more you should doubt it.

It’s always useful when your ideological opponents drive their arguments over the edge of reason — it saves a lot of debunking.

Thomas Piketty’s done us all a service by really following through on the implications of his own ideas, boarding the reductio ad absurdum train and absolutely, positively refusing to get off until the final stop.

In the Global Justice Report — launched last week at his World Inequality Lab’s big Paris conference — Piketty argues that drastic action is needed to curb global emissions enough to keep the planet habitable. As the coordination problem is global in scale, the authority that leads the response will need to be global too: to wit, a Global Justice Fund with full fiscal powers and an aggressive agenda to massively redistribute global income.

He wants the Fund to absorb around 10% of world GDP a year (~$12 trillion, bigger than the German and Japanese economies combined), and cut annual working hours from ~2,100 to ~1,000 per worker.

He doesn’t call it a world government, but that’s a world government.

A big part of the point is supposed to be to keep the world habitable, which the report equates with with a call for very fast emissions reductions. This implies not just a global government, but one powerful and independent enough to impose a radical agenda to deliver them. This demands not just increasing the rate at which advanced economies are decarbonizing but also deep cuts in emissions from poor countries.

You can dress it up in all the progressive phraseology you want, but the reality is that this would mean deepening poverty for billions of people in the developing world. Given a choice, voters in the developing world will never vote for this: it will have to be imposed on them.

Look, Piketty’s analysis is not wrong, exactly; just crazy. He’s right that if you want to regulate a negative externality at the global level, you’re going to need some kind of global sovereign authority to achieve that.

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It’s precisely the fact that there isn’t any such thing as a global authority that makes responding to climate change hard. The limp mechanism we have for coordinating action between Westphalian states — the UN — definitely is not a global sovereign, which is why its attempt to fit the round peg of restricting greenhouse gas emissions into the square hole of voluntary coordination between formally equal and sovereign states hasn’t worked, doesn’t work and won’t work.

If your one policy response to climate change is drastic emissions reductions, then you can’t do it without a world government. It’s just that a sane person looks at that sentence, realizes “oh, but there isn’t the slightest sliver of a chance we’re going to get a world government anytime soon,” and draws the obvious conclusion: we’re never going to get drastic emissions reductions, period.

This is one of those very obvious things people resist saying because we’ve been taught it’s the end of the world. That it’s plainly true, that all the data show it’s true, that economic theory and political common sense support it, that the yearly farce that is COP illustrates it, that deep down we all know it’s true doesn’t make it more sayable. That’s how taboos are: things we don’t say because they point at truths that are too unpalatable. Markers of chosen ignorance.

Thomas Piketty has just put himself through the ordeal of writing a whole fancy report to pretend that this very obviously true thing isn’t true, and that a world government is a live possibility, and that it should be led by people who think just like him for the purpose of delivering on his agenda.

The report calls for the Global Justice Fund to be “governed by strict rules of democracy and transparency”, but then also wants it to prioritize degrowth. What happens when the world’s voters refuse to vote for GJF leaders who promise to make them poorer is one of the many, many obvious objections the report artlessly elides.

Look, to deliver on the goals set out for it, the GJF would have to act as a kind of global dictatorship: imposing policies that voters would never back, policies favored exclusively, as far as I can tell, by a minuscule elite of first-world degrowther intellectuals who hang out with Thomas Piketty — so maybe not the most promising basis for stable world government.

The entire thing is harebrained and stupid in the kind of way only someone locked inside a hermetically sealed echo chamber could fail to notice. It’s just ridiculous.

But I’m indebted to Piketty for following the degrowth agenda through to its utmost consequences — and just sort of mystified he doesn’t seem to realize he’s debunking his own agenda a lot more convincingly than I ever could.

Because, again, Piketty is not wrong; just crazy. He’s right that without a world government, emissions are going to peak sometime in the next ten years, then fall too slowly to meet our Paris Agreement targets.

The smart response to that isn’t despair, it’s realizing that emissions are the wrong policy target. We can get at the problem in other ways — ways that don’t require cheerleading for a global envirodictatorship.

Developing pathways for carbon dioxide removal at scale won’t scratch Thomas Piketty’s Central Planning itch, of course. It won’t gel with his watermelon politics — all green on the outside, red inside. What it will do is solve the problem. Which, y’know, oughta count for something.

Say you read my last post and you agree cost is sorta the whole ballgame when it comes to carbon dioxide removal. The question is, ok, so what’s going to be the lowest-cost method?

The easy answer —we don’t know yet!— is both true and unhelpful. It’s true because the way you find out what something costs is by implementing it at scale and then optimizing that implementation: that’s where the big learning-by-doing economies come in, and that’s not something you can simulate ahead of time. It’s unhelpful because it doesn’t guide our decision-making at all.

We don’t know yet, that’s true, but we can make some educated guesses. To make those guesses, you have to understand where the cost drivers are for carbon dioxide removal. Basically, there are two: the cost of capturing carbon dioxide, and the cost of storing it safely away from the atmosphere.

These vary a lot by method. Many methods proposed use energy for the capture part — which figures: the reason we burn hydrocarbons in the first place is that they release energy as they produce carbon dioxide. If you want to run that reaction in reverse, obviously it’s going to require energy. And energy is expensive.

For many electrochemical methods — direct air capture, electrochemical ocean alkalinity enhancement, etc.— energy costs tend to dominate the cost picture. And because the core variables in this equation are hard-coded into the laws of thermodynamics, there are relatively high price floors involved unless energy becomes much cheaper (which, let’s hope it does!) Other methods, like enhanced rock weathering, rely more on chemistry for the capture — but to get that chemistry to work you have to mine and crush and spread huge quantities of minerals, and that has an energy cost of its own.

But once you’ve done the capture, you’re now left sitting on a large quantity of carbon dioxide that you have to store somehow. There are some clever ideas out there to store it in plain sight, locked inside building materials, for instance. But for many methods, storage is another expensive proposition: you have to build the industrial infrastructure to inject the carbon dioxide into depleted oil wells, say, or you have to literally bury it in a hole you’ve dug in the ground. Those things cost money.

If you’re going to seriously drive down the cost of carbon dioxide removal to the kind of $5-$25 per ton region where you’d need it to be to make implementation at scale feasible, you need some kind of workaround, some way to bring both the energy cost of capture and the cost of storage down to near-zero.

That sounds like a pipedream. But it isn’t. It is possible, if you leave the job to tiny marine plants.

Phytoplankton —microscopic plants in the ocean— daintily sidestep both of the cost drivers that make most carbon dioxide removal uneconomic. Capture relies on photosynthesis, which is solar powered and therefore literally free. And storage relies on particles sinking through the water column, which is just gravity, which last I checked, was also free.

With $0 to pay for capture and $0 to pay for storage, phytoplankton carbon solutions begin life with an insurmountable cost advantage over other capture methods. The actual costs end up being associated with the actual minerals you’d need to add nutrients to marine deserts, but because you’re mostly talking about modest quantities of cheap minerals like iron, those just don’t add up to very much: no more than $5 per ton, and potentially as little as a few pennies. That leaves the cost of deployment — the boats and crews and such — and the cost of scientific monitoring, reporting and verification of carbon transport. Where that ends up settling once you scale is really uncertain, but there’s no a priori reason why it can’t settle at $25 a ton, or potentially quite a bit less.

This is why I tend to think we should spend all our time developing Phytoplankton Carbon. It has a clear, credible path at delivering a sub-$25 ton of carbon dioxide removal that’s both ecologically sound and long-lasting. It can do this because it puts two big fat zeros in the Excel cell where most CDR methods have the bulk of their costs: capture energy and storage.

Maybe there’s some other technique that can match that. If there is, I haven’t heard of it.

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Say you’re the chief sustainability officer for United Airlines. Or Lafarge, the French cement giant. Or Nippon Steel. Or basically any big polluter in a sector where abating emissions is difficult.

You have a bunch of engineers working for you, and part of their job is calculating what it will take to abate your climate emissions. Because you’re in a hard-to-abate industry, the costs they’re going to report to you are going to be high — that’s sort of the definition of hard-to-abate. In aviation, the marginal cost of lowering emissions comes in around $300-$400 per ton of CO₂ — which is a lot because, well, Sustainable Aviation Fuel prices are sort of murder.

In cement, you’re looking at sort of the $80-$240 range per ton for CCS, depending on a whole lot of factors. In steel, you’re again looking at sort of $90-$200 per ton or so. These are the marginal costs of abating the next ton of CO₂ — the average costs of abating your entire carbon footprint would certainly be higher.

For simplicity’s sake, let’s say in your company, the engineers tell you the marginal cost of abating the next ton is $100. And let’s say your sustainability budget also happens to be $100.

Now, say you look at the offset market, and an entrant has figured out technology for a high quality, long-term ton of carbon dioxide removal that costs $50. What should you do?

Well, you could say your primary responsibility is for your company’s own emissions, so you’re going to abate those first. You could spend your $100 budget abating one ton of CO₂. Of course, that means you don’t pay that new CDR company $100 to draw down two tons of CO₂. The opportunity cost of your decision, then, is to leave one ton of CO₂ in the atmosphere that you could have taken out of it.

Is this reasonable environmental stewardship?

I don’t think it is. I think if you’re really focused on carbon dioxide concentrations in the atmosphere, the logical thing to do is to buy the offsets. Given your budget constraint, economic rationality demands that you focus your resources on the pathway that will have the greatest impact.

The logic of this seems, to me, fairly obvious. And yet when I tell people I’m working on low-cost carbon dioxide removal options, one of the objections I hear most often is “but isn’t that just giving polluters an excuse not to decarbonize?”

Now in the carbon removal world, the standard reply to that objection is “no of course we know we need to decarbonize. We’re not proposing an alternative to decarbonization, we’re proposing an addition to it.” Which, I think, sounds nice and makes you come across as environmentally conscious and respectable and solidly within-the-consensus.

But more and more, I find myself questioning that answer. Because it is economically illiterate.

The atmosphere, for its part, is entirely indifferent between a ton of carbon dioxide that’s been removed and one that was never emitted in the first place. It’s not that one has a bigger impact than the other. It’s the overall level of carbon dioxide in the atmosphere that causes warming: a ton is a ton is a ton.

If you accept that, you come to see that the insistence on prioritizing emissions reductions over carbon removal is entirely arbitrary: more an expression of a kind of free-floating hostility to industrial civilization than anything you can really defend on climate terms.

What the world needs now is a $10 ton of safe, long-term carbon dioxide removal. Once we have a truly low-cost, high-quality, scalable technology for taking carbon out of the atmosphere, some things that are now obscure will become crystal clear. If we had a $10 ton, then abating all 40 billion tons of carbon dioxide we’re now emitting each year would become a $400 billion a year proposition.

That’s a lot of money, yes, but it’s not actually that much money in the scheme of things.

Total current spending on climate mitigation and adaptation has been estimated at north of $1 trillion. Which means if we had a $10 ton of removals, we would be able to save $600 billion a year and actually reach Net Zero, rather than what we’re doing now, which is spending more than twice that much without actually solving the problem.

Look, I know there are powerful conventions preventing us from really developing this kind of reasoning. I understand it makes people uncomfortable. I get it that emissions reductions have been fetishized to such an extent that people see punishing polluters as a kind of inherent goal of climate policy.

But this has it backwards. United Airlines doesn’t pollute a lot because they’re bad people, they pollute a lot because you and I want to fly in airplanes. Lafarge doesn’t pollute a lot because they’re irredeamable fat cats, they pollute a lot because you and I demand infrastructure that can only be built with cement. Nippon Steel doesn’t pollute a lot because they’re indifferent to the environment, they pollute a lot because every day of the year you and I use things that can only be made with steel.

Emissions are there because you and I benefit from products and services that generate emissions.

My focus is on carbon dioxide concentrations in the atmosphere. If we recenter the climate debate on what actually matters to the climate, we’ll see clearly that there’s more than one way to bring those concentrations down. We’ll accept the obvious reality that our willingness to pay to abate climate change is limited, and that when your resources are limited rationality demands that you concentrate them on their most efficient uses.

Which is why developing a long-duration, low-cost method of capturing carbon dioxide from the atmosphere is where our focus should be as climate activist. The rest might make us feel good, but it won’t make a difference.

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Remember the climate crisis? Bet you don’t. For the average news consumer, climate has fallen dramatically in salience this year.

Which kind of figures: the world is on fire.

A deranged American president launched a war he can’t explain that now threatens a global economic calamity. The global order is no such thing, and AI is racing towards the realm of the truly weird much faster than people guessed even just a year ago. It’s…not an environment that’s conducive to fretting about climate, is it?

Not everybody’s thrown in the towel, of course. The Guardian still has a Climate Crisis vertical, and plenty of outlets do still try to keep up some climate reporting. Yet when the Washington Post fired fourteen climate reporters in February, the story barely registered. Everybody recognized that the vibe had well and truly shifted, and honestly with [gestures broadly] all that going on, worrying about climate feels like a bit of a specialist interest, doesn’t it?

Look, I’m a climate guy. I work on climate, I spend all day every day thinking about this stuff. So you might expect me to be distraught about its disappearance from the discourse. I’m not, though. Because I know the public’s basic response to the shitshow that is 2026 is, strictly speaking, quite rational.

For all the time and effort (and money) spent by the activist community to convince us that climate is an acute emergency, most people understand that the biggest risks associated with climate change are long term. Genuinely catastrophic outcomes are very much in the cards — and very much more likely to upend the lives of your great grandchildren than yours.

People discount the far future; they always will. Discounting the far future is fully rational. Doing so more aggressively when you’re in the middle of an acute crisis is also fully rational. Your high blood pressure may be a genuine, serious health problem, but if you’ve just been shot in the thigh you’d be insane to prioritize it right this minute.

That’s just the way the world works, and if we allow ourselves to think about it dispassionately, I don’t think any of us would seriously dispute that.

As a climate activist, I don’t think these realities are reasons for inaction, much less for despair. I try to accept them as a given: just the shape of the information space we operate in.

We don’t actually get to change it, and if we try —by launching, say, an ill-judged information campaign to convince people to write “climate crisis” instead of “climate change”— all we’ll do is raise the public’s skepticism. People know when they’re being hoodwinked.

The willingness to take a cold, hard look at these realities has come to be associated with the denialist right: people like Chris Wright who want to make it an excuse to do nothing. That’s not a defensible position either, I don’t think. Intuition screams at us that leaving an unlivable planet to the people of the 22nd century is wrong, even if you and I won’t be there to deal with the consequences

Instead, I try to think honestly about what we can do about a hugely consequential problem that most people quite rationally do not prioritize.

That people will not and should not prioritize climate has troubling consequences. For one, it means we’re not likely to see dramatic reductions in greenhouse gas emissions anytime soon. Yes, emissions may peak in the next ten years or so and start to abate slowly, but that’s very different from the kind of drastic, fast reductions needed to reach net zero quickly enough to keep warming to within 2 degrees of the pre-industrial baseline.

Such abrupt reductions would be just about imaginable if people really did see climate as a crisis in the same way they see the Strait of Hormuz crisis as a crisis. But they don’t, and they won’t, because it isn’t.

People will not support a drastic changes in their lifestyles, much less dramatic reduction in their standard of living, to prevent big harms in 80 years. Thinking we can persuade them to do that is a fool’s errand. It would be irrational and self-harming and they won’t do it, and the sooner we accept that, the sooner we can move into an honest conversation about what we can do.

This is why I spend all my time working on heterodox responses to climate change.

Albedo modification and marine Climate Dioxide Removal are the only responses to the climate crisis that align the public’s actual level of concern with a program of action we can really implement.

These heterodox responses allow us to meet people where they are — to tell them, honestly — “look, I get it: this is a concern for you, but it’s not the concern. You’re not going to turn your life upside down to respond to it, nor should you. Still, it’s madness to just ignore it, so let’s have an honest conversation about the things we can do without nuking your lifestyle, or your budget.”

Traditional environmentalists will see that as waving a white flag. It’s certainly not that. It’s a grown-up response to a problem that’s proven to be beyond the reach of juvenile antics.

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I tried to vibecode an app the other day.

It did not go well.

I’m not a coder, so I didn’t really know how to prompt the AI precisely enough to get it to do what I wanted. It spat out a thing that wasn’t really what I wanted, and because I’m not a coder, I didn’t know how to get it to change it into the thing I did want.

Some sort of app did come out the other end. It sucks.

The wrong lesson to take from that experience is “AI is bad at coding.” Software engineers all seem to find that AI is incredibly good at coding. It’s just that to get AI to code well, you sort of have to know how to code yourself. If you heard a software engineer say they think AI is terrible at coding, you’d probably think to yourself “this guy isn’t very good at coding.” And you’d probably be right.

It’s the same thing for writing.

I write with AI all the time. Every day, really.

It’s just that, I’m a writer. I’ve been doing it professionally for 25 years. When AI gives me a garbage output, I can spot where the garbagefulness resides right away. I know exactly what good writing is, so I know precisely how to prompt AI when it messes up.

People who complain AI is bad at writing are sort of telling on themselves. If you’re bad at writing, AI won’t help you much. It’ll clean up your sentences, sure: hunt for typos, give your garbage input some kind of superficial sheen. But it won’t make it good.

If you’re good at writing, AI is hugely liberating. My workflow now consists of a series of very intensive collaborations with Claude. I’ll work up a draft, upload it. Ask it to pick it apart. Consider the feedback, pick apart the good advice from the bad. Rewrite and upload again, ask him to suggest a better way of expressing this point or that, consider it, then tweak it and keep it or chuck it out fearlessly, because the robot never takes an edit personally. I’ll keep iterating, taking advantage of Claude’s true killer feature: indefatigableness. It can keep spotting typos on the 18th iteration, long after any human editor’s eyes would’ve gone dead. I’ll be insanely picky, because the robot doesn’t mind.

Then I’ll ask it to fact check, and to fix any mistakes. Then I’ll ask it to read it oppositionally, looking for weaknesses a critic might attack or imprecisions that might confuse someone. I’ll rewrite again, and check again. On my own this would take an unfeasibly long time, but the robot is fast, and it doesn’t get tired.

And I’ll ask it to help me identify the people I’d need to interview to really make sure it’s right, then I’ll put in a call to that person to check. I don’t expect the robot to replace reporting, I expect it to take the pain out of reporting.

What comes out at the end of this process is unambiguously better than what I could’ve written on my own in a comparable span of time. I might have been able to get to that same level on my own if I had 60 hours to throw at a piece, but I don’t. I have 3 or 4. The end product is fully mine: even if not every word on the page is one I wrote, every word on the page is one I closely scrutinized.

If you’re a writer, Claude can make you a better writer. If you’re not a writer, it can’t do magic. If you have a half-baked idea, prompt the AI sloppily once then copy and paste its first response into the Substack window, you’re debasing the discourse.

But you’re not proving AI is bad at writing. You’re proving you’re bad at writing.

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Your house looked something like this:

Your parents scrimped and saved to put you through school, and you were determined their sacrifice wasn’t going to be for nothing. You studied hard, and you did well. You finished high school, went on to technical training, learned things no one in your family had ever known, qualified for jobs much better than they could have had.

And you’ve done well. Well enough to help your aging parents now. Well enough to afford things they never could—meat when it’s not a holiday, trips to see them once or twice a year. You bought a window air conditioner on installments for those days when it gets really hot. Which come more and more often.

You have a good job now.

After years in a cramped apartment, you even qualified for a mortgage.

Your house looks something like this:

You’re nobody’s idea of rich. You’re one work accident away from losing it all. But you’re not poor in the way your parents were. You sleep on a foam mattress you got at a store, not on straw. Your kids don’t cry themselves to bed hungry. Things get tight at the end of the month, but you’re making it.

Maybe your job is in Lagos. Or Guayaquil, or Dhaka, or Chongqing. The farm where you grew up may have been in Nigeria, or Ecuador, or Bangladesh, or China. Probably China.

The thing is, you are not alone. There are billions of people like you, worldwide, who grew up very poor and now have a foothold in the global lower middle class.

Individually, each of you generates a fraction of the greenhouse gases the lifestyle of the average person in a rich country does. But there are many times more of you than there are people in rich countries. Which is why global emissions keep rising, even though emissions from rich countries keep falling.

People in rich countries aren’t ready to face what your rise means.

We aren’t ready to accept that for millions of people like you, being less poor and consuming more stuff are pretty much synonyms. We don’t want to face the reality that when your consumption goes from near zero to not a lot, emissions rise.

This is about much more than where you get your power. Sure, solar panels are cheaper than ever. But you’re not just buying electricity. You’re buying a scooter to get to work instead of taking the bus. You’re buying a refrigerator so food doesn’t spoil. You’re replacing your corrugated metal roof with concrete. You’re taking the bus to visit your parents instead of walking. You shudder when you remember a childhood of eating just one staple grain meal after meal, and you treasure the variety of foods you can now afford: vegetables, processed foods and, yes, meat.

Rising into the global lower middle class means using more of everything—concrete, steel, transportation, food.

Every step up from poverty is built on physical stuff. And making physical stuff, moving physical stuff, keeping physical stuff cold—that’s where the emissions are. The electricity to power your lights is almost incidental.

The solar panels on your roof don’t change the fact that you bought a roof. They don’t change the emissions from the concrete plant, the steel mill, the scooter factory, the truck that delivered your refrigerator, the industrial farming that produces your chicken.

We aren’t ready to face the reality that you-being-less-poor and you-emitting-more-carbon are sides of the sane coin—not because you’re buying dirty electricity, but because you’re finally able to buy things at all.

Of everything the first-world climate commentariat is in denial about—and there’s a lot—this is the big one: that rising global emissions have little to do with what happens in the rich countries. They keep soothing themselves with misleading headlines about half of the world’s CO2 emissions coming from just 36 fossil fuel firms, as though those firms were emitting for the sake of emitting, instead of serving the demand from people like you.

Deep down, though, they must know that the story of rising global emissions are the story of you getting less poor.

We’re desperate for this not to be true. We want a villain we can properly hate. We want Climate Justice to mean sticking it to capitalist pigs, not reckoning with the fact that emissions are rising because billions of the world’s poorest people have lives incomparably better than their parents did.

We want the baddie to be someone easy to hate.

You’re not. So we don’t think about you at all.

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Look at this bad boy.

It’s the Newton.

Apple launched it in 1993. Nerds and analysts ranted and raved about it. It could recognize your handwriting! It could keep your calendar and your contacts! To a lot of people at the time, this was the future. But this wasn’t the future.

Camera? Sharight. The Newton could not connect to the internet, because there was no internet to connect to. It was a complete failure commercially. The iPhone would come along fourteen years later, wipe the canvas clean, and establish a new paradigm.

Carbon dioxide removal is in its Newton era. We have a bunch of clunky technologies that aren’t it, and we spend a lot of time trying to perfect them. Because we see a shiny future off in the distance and we want to get closer to it.

Right now we’re looking at direct air capture systems that cost around $1,000 per ton, maybe headed toward $600, maybe eventually $100 if a series of engineering (and, hell, thermodynamic) miracles materialize in the coming decades. Enhanced rock weathering might get down to $200. Biochar, maybe $150 on a good day with generous carbon accounting. OAE hoping for sub $100 tons one day, if the stars align.

The technologies are real: they work, people are deploying them. But at those prices, the market that exists is tiny and artificial. It’s Microsoft making commitments for demonstration projects that look great on a Corporate Sustainability report. All of this is subsidy-dependent or driven by corporate climate pledges that amount to sophisticated PR. It’s not a real market.

For lots of carbon removal people, the working assumption is that the way you get to an iPhone is by making a Newton 10% better year after year.

That’s…not how this works.

Multi-gigaton carbon removal is not going to happen by making DAC fans 15% more efficient or scaling up biochar production or testing enhanced weathering on larger acreage. These are real improvements: brilliant engineers are working hard on them right now. But they’re refinements on existing approaches that have hard cost floors and fixed scalability ceilings.

The urge to optimize what exists is strong. But every minute we spend optimizing our Newton is a minute we’re not spending developing our iPhone.

The iPhone didn’t just win the existing cell phone market. It created an entirely new market by solving problems the previous generation of designers couldn’t solve.

Cheap carbon removal will do the same thing. At $1,000 per ton, the only buyers are true believers and regulatory compliance. At $100 per ton, you get serious corporate purchases and maybe some government programs. But at $10 per ton, removing a ton of carbon ends up being cheaper than abating emissions in many cases. Why spend the $50 it takes for electrified heavy trucking to prevent one ton of carbon dioxide if that same $50 can buy you five tons of removals?

To get to genuinely low-cost removals, we need to be a bit ruthless. Devoting more time and more money to elegant approaches that won’t scale isn’t going to do the climate a lick of good. Here, I’m with Ocean Visions: if your carbon removal method doesn’t have a clear path to multiple-gigatons-per-year scale, you need to rethink. Because high cost approaches amount to fancy corporate PR, not climate work.

The carbon removal sector that exists blinds us to the shape of the one that will exist.

To bring it into existence, we need to focus on approaches that aren’t refinements of existing methods but genuine reconceptualizations of the problem. That means focusing on the projects that sound weird or implausible or too ambitious. The ones that aren’t trying to make biochar 20% cheaper but are asking entirely different questions about how to interact with the carbon cycle.

If you read this substack, you know the general direction I expect those ideas to come from. But that’s not really what this is about. Because maybe I’m wrong: maybe the avenue that gets you to $10 a ton is not the one I’m thinking of at all.

My sense is that the people building the transformative solutions aren’t visible yet. They’re too early. Too weird. Too unproven. They’re in a lab probably, or on a ship, thinking ideas that strike people as way out there.

If that’s you, keep going. And reach out if you want to chat. And if you’re looking for someone doing this, try to find weird people saying weird counterintuitive things, or most likely working quietly and not saying anything at all.

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For an 84 year old, James Hansen has a remarkable knack for stirring the pot. The man who first brought Climate Change into the public imagination remains one of the planet’s most closely watched climate scientists. But rather than settling comfortably into the climate science mainstream he once embodied, he’s become an increasingly ardent critic: slamming mainstream science for dramatically underestimating the amount of warming Earth is likely to face.

His latest hobby horse? The El Niño cycle is all out of whack.

But first, here’s the lay of the land for this controversy: the Intergovernmental Panel on Climate Change — the IPCC, the body that synthesizes the global scientific consensus on climate — estimates that if you doubled the amount of CO₂ in the atmosphere, the planet would eventually warm by about 3°C. Jim Hansen says it’s at least 4°C.

What the earth’s actual “climate sensitivity” is matters enormously. If Hansen is right and the IPCC is wrong, we’re in for a much rougher climate ride than we’ve realized.

The debate is wonky, and can come across as irresolvable: one set of nerds has one set of numbers, another set has another set, the math behind each is baffling and you have no way to tell who’s right.

Except Hansen thinks he can prove he’s right not someday in the far future, but before the next summer Olympics. That’s why he’s put a specific, falsifiable prediction on the table: global temperatures, measured as a 12-month running mean, will bottom out at around 1.4°C above pre-industrial levels in early 2026 — during the current La Niña — and then rise to around 1.7°C by early 2027, as the next El Niño kicks in.

If that happens, he argues, it’s game over for the low-sensitivity models.

What’s an El Niño Got to Do With It?

Think of the tropical Pacific Ocean as a giant bathtub that sloshes back and forth. Normally, trade winds push warm surface water westward, toward Indonesia and Australia. Cold water wells up near South America to replace it. That’s La Niña — the cool phase.

But sometimes the winds weaken or reverse. Warm water sloshes back east. The cold upwelling stops. Heat that was stored in the ocean escapes into the atmosphere, and global temperatures spike. That’s El Niño.

El Niños don’t cause global warming — they temporarily reveal heat the ocean has been storing. It’s like opening the oven door: the kitchen gets hotter, but the heat was already there. What makes them useful for Hansen’s argument is that they act as a natural stress test. An El Niño forces the climate system to show its hand.

The thing is: we just had one. The 2023-24 El Niño ended barely two years ago. Normally, the ocean needs longer than that to recharge — to rebuild the pool of warm water in the western Pacific that fuels the next event. In the last 75 years, no strong El Niño has followed another one this quickly.

So if a substantial El Niño develops in 2026 anyway, that itself is a signal. It would suggest the ocean is accumulating heat faster than it used to.

The Aerosol Dimension

The standard story of global warming is straightforward: we emit greenhouse gases, they trap heat, the planet warms. But there’s a hidden variable that typically gets snipped out of the picture: aerosols.

When we burn fossil fuels, we don’t just produce CO₂. We also produce sulfur dioxide and soot and other particulate matter that drifts into the atmosphere and ends up cooling the planet by reflecting solar radiation back out to space. Aerosols also seed cloud formation, and clouds reflect sunlight too. For decades, this aerosol cooling has been partially masking the full warming effect of greenhouse gases: like we’ve been running the heating and the air conditioning at the same time.

Starting around 2015, aerosol emissions began to drop — fast. Mostly, this was good news: China launched an aggressive clean-air campaign that dramatically cut sulfur dioxide emissions and prevented many, many Chinese people from dying horrible deaths from respiratory illnesses caused by air pollution. But it also cut down on the reflective aerosol particles that were offsetting some of our global warming.

Then, in 2020, new international regulations forced the shipping industry to switch to cleaner fuels, cutting sulfate emissions from cargo ships. That, again, turned down the air conditioning.

Hansen argues that this reduction in aerosol cooling is a major reason global temperatures have surged in recent years. It’s not just that greenhouse gas forcing has increased — which it has, by about 20% between 2010 and 2015. It’s that the aerosol mask has been ripped away. And if you put those two things together — higher sensitivity and reduced aerosol cooling — you get a planet warming much faster than the standard models predict.

Why the IPCC Gets It Wrong (If Hansen Is Right)

Hansen charges the IPCC with relying heavily on Global Climate Models — massive computer simulations that try to capture the physics of the atmosphere and oceans. These models handle some things well. They simulate water vapor feedback accurately, for instance. But Hansen argues they systematically underestimate cloud feedback — the way warming changes cloud cover in ways that amplify further warming. Clouds are fiendishly hard to model. They form and dissipate at scales smaller than most climate models can resolve. They’re the source of most of the fat error bars around the IPCC’s climate sensitivity estimates. They know they don’t know how to model them. Hansen thinks if they modeled them right, they’d realize we’re in way deeper shit than we realize we are.

IPCC models produce a climate sensitivity centered around 3°C — not because the physics demands it, but because the models can’t fully capture the feedback loops that would push it higher. Hansen points to four independent lines of evidence — paleoclimate data, observed warming patterns, ocean heat content, and direct measurement of Earth’s energy imbalance — that all converge on a sensitivity of at least 4°C.

The IPCC, he says, has been giving too much weight to models and not enough to observations.

So what happens now?

As of early 2026, the tropical Pacific is in a La Niña phase — the cool side of the cycle. But climate models and recent wind patterns suggest a transition to El Niño later this year. Westerly wind anomalies over the past month have been weakening the trade winds, allowing warm water to slosh back eastward. If these wind patterns persist through the northern hemisphere spring, a substantial El Niño could develop by summer.

Hansen is characteristically blunt about what this means. If global temperatures bottom out around 1.4°C during this La Niña — a level higher than any El Niño peak in the decade before 2023 — that alone would be powerful evidence that global warming is accelerating sharply. He bolsters the case by noting that the 12-month running mean of tropical Pacific upper ocean heat has a correlation of more than 50% with running-mean global temperature, “leading global temperature by 9 months,” while the Nino3.4 index — the standard El Niño measure — has “slightly higher correlation, but a lead time of only 4 months.” (If your eyes just glazed over, welcome to the James Hansen reading experience.)

Hansen is saying the ocean data he’s tracking is already flashing warm. If temperatures then rise to 1.7°C during the next El Niño, it would be very difficult to explain without invoking high climate sensitivity and reduced aerosol cooling — because, as Hansen puts it, climate feedbacks “do not come into play in direct response to a climate forcing, but rather in response to the (delayed) temperature change caused by the forcing,” and it’s precisely those feedbacks that “distinguish high sensitivity from low sensitivity.” Translation: give it a year or two after an El Niño, and the temperature response will diverge sharply depending on whose models are right. It’s easy to get lost in the details, the point is that the La Niña trough we’re in now is already inconsistent with IPCC models, and the El Niño peak we’re about to experience will be even more so.

“This is the sort of bet,” Hansen writes, “that one prefers to lose.”

Please, God, let Hansen be wrong

Let’s be clear about what it means if Hansen is right.

It means 2°C of warming — the threshold the Paris Agreement was designed to prevent — arrives in the 2030s, not mid-century. It means the window for meaningful climate action is considerably narrower than most policymakers assume. It means the comfortable framing of “we have until 2050” — which already felt optimistic — is just flat-out wrong.

Jim Hansen has been sounding the climate alarm since his famous 1988 congressional testimony, and he’s had a better forecasting record than the mainstream consensus for nearly four decades. His contempt for colleagues who disagree with him can be grating — he accuses the climate establishment of responding to his papers in “juvenile, unscientific fashion,” which is not exactly how you build coalitions. But he has a track record that demands attention, even when — especially when — his conclusions are uncomfortable.

I hate it that his ideas are trapped inside prose that only specialists can parse. If you’ve ever tried to read one of his Substack posts, you know the experience: you start with genuine interest, hit a wall of acronyms and chart descriptions around paragraph four, and emerge twenty minutes later unsure what you just read but vaguely anxious.

What he’s saying, stripped of the jargon, is that we have less time than we think, the evidence is about to become undeniable, and the climate science establishment needs to get its shit together and face this. Whether you find that credible or alarmist, the next eighteen months of temperature data will bring a clarity this discussion is sorely in need of.

Because the thermometer doesn’t care about anyone’s writing style.

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For the better part of fifteen years, ocean fertilization has been stuck in a peculiar limbo—too promising to ignore, too controversial to fund, too uncertain to deploy. To phytoplankton obsessives like me, it’s been an intolerable state of affairs. Last week, though, brought the promise of a reprieve from this limbo, in the form of the thing we crave most: big time validation from the institutional mainstream.

Ocean Visions —the nonprofit that’s become the closest thing the marine Carbon Dioxide Removal world has to a central nervous system—just released its Phytoplankton Carbon Solutions Research Framework, a landmark 47-page blueprint for how to investigate whether boosting the ocean’s biological carbon pump could actually work as a climate-relevant mCDR strategy. And not in the hand-wavy, wouldn’t-it-be-nice way that ocean fertilization has been talked about since the 1990s, but in a rigorous, stage-gated, outcome-agnostic way that can bring big time donors on board.

This is a big deal.

Ocean Visions isn’t some scrappy startup with a pitch deck and a prayer. Founded in 2020 with backing from the Grantham Environmental Trust and ClimateWorks Foundation, it’s become the field-building hub for marine CDR, sitting at the center of a network of leading oceanographic institutions and universities. Their CEO, Brad Ack, and chief scientist, David Koweek, have been methodically assembling the infrastructure—roadmaps, databases, assessment frameworks—that a serious research field needs to actually function.

And the money behind this particular report? The Ocean Resilience and Climate Alliance, better known as ORCA—a $250 million philanthropic coalition whose funders read like a who’s-who of serious climate money. Bloomberg Philanthropies. The Sergey Brin Family Foundation. The Packard Foundation. The Moore Foundation. Builders Vision (that’s Lukas Walton, i.e., Walmart money). Oceankind. The Grantham Trust, which leads ORCA’s mCDR pillar specifically.

We’re way past the fringe here. This is the institutional climate philanthropy establishment saying: we think this question deserves a serious answer.

The report itself was guided by an international advisory board, workshopped with 67 experts at the Ocean Visions Biennial Summit in Vancouver, and put through a 30-day public comment period that drew feedback from 56 individuals. We’re far beyond vibes here.

Ocean Visions starts by introducing a useful umbrella term—”Phytoplankton Carbon Solutions,” or PCS— that goes beyond just traditional ocean iron fertilization in High Nutrient, Low Chlorophyll cold water ecosystems — what I think of as GOFOIF (Good Old Fashioned OIF.)

Phytoplankton Carbon Solutions includes a broader family of approaches that leverage the biological carbon pump for CDR. This includes new approaches like nitrogen-fixation in low-nutrient (subtropical) waters, macronutrient fertilization, artificial upwelling, and newer categories like export-based approaches that enhance how much organic carbon sinks down to the deep ocean.

GOFOIF is still the headliner, simply because it’s been trialed already so we have some solid idea of how it would work. Idealized models suggest it has multi-gigaton gigatons removal potential, and its leverage ratio is extraordinary: one unit of iron could theoretically remove hundreds to tens of thousands of units of carbon from the surface ocean.

But the report makes it clear that Ocean Visions is still reserving judgment on whether GOFOIF can actually work in practice. Their cost estimates for OIF range from less than $25 to more than $53,000 per ton of CO₂, which is not a cost estimate, more like a confession of ignorance. Kudos to Ocean Visions for refusing to pretend to have answers they don’t yet have. The challenge for the field now is to constrain that uncertainty.

The report’s most consequential contribution here may be the four-stage decision framework for how to move these ideas forward.

Stage 1 is Pathway Characterization: define the mechanics, quantify the uncertainties, identify the risks. Basically, does this idea even make sense? Stage 2, Pathway Refinement, is where you start doing real science — model improvements, natural analog studies, small-scale field trials up to 100 tons of iron over 1,000 km², and serious community engagement. Stage 3, Evidence for Scale Up, is where it gets expensive and where you find out if your models were lying to you: large-scale field trials with over 100 tons of iron across 1,000+ km², rigorous MRV validation, co-designed research with affected communities, and full regulatory compliance. Stage 4, Deployment Optimization, is our shangri-la: gigaton-scale operations, independent standards development, and the kind of broad international public support that, let’s be honest, no ocean intervention has ever come close to achieving.

Each gate requires clearing specific feasibility and desirability hurdles before more money flows. What they’re building is a funnel designed to kill bad ideas early and cheap, before they become bad ideas that are late and expensive — a concept that, come to think of it, would save us all a lot of grief if applied more broadly in climate policy.

They’re thinking in a structured way about what research to back and what research to step away, so they lay out specific criteria a PCS pathway should meet to advance to the next level of investment. To keep backing a thing, they want to make sure it has a clear pathway to:

1. Durability of at least 100 years.

2. Measurability on par with other CDR pathways.

3. Potential to reach a gigaton per year of CDR for multiple decades.

4. Cost trajectory toward $100 per ton or less.

5. Sufficient understanding of environmental and socio-economic risks to support informed decision-making.

6. Social and regulatory support from affected communities.

The flipside is that the approach builds in explicit offramps. If scalability potential drops below a gigaton per year, if there’s no feasible path to reduce uncertainty, if environmental risks prove insurmountable—you stop. This is exactly the kind of disciplined, outcome-agnostic structure the field has needed. Because the phytoplankton world needs advocates —a role I’m super happy to play— but it can’t be just about advocacy: the money people need a decision architecture, a structured way to tell if the light is green, yellow or red.

Currently, only GOFOIF qualifies for Stage 2 (Pathway Refinement), based on the knowledge built up through 15 field experiments between the 1990s and 2009. Everything else—LNLC iron fertilization, export innovations, macronutrient approaches—sits in Stage 1 (Pathway Characterization). No field trial has been conducted since 2009, when a rogue commercial operation in the Pacific poisoned the well for a generation of research.

Ocean Visions is definitely right that we need to reduce uncertainty in net CDR estimates and, especially, the biogeochemical models behind those estimates. This is my current main obsession: right now, models don’t agree on basic questions about fertilization’s carbon benefits, so we certainly can’t have that. The report does note we’d be much better off if we understood the nitty gritty of the biological carbon pump’s baseline behavior better. I know it sounds like motherhood and apple pie, but it matters.

The most exciting part is that Ocean Visions comes out emphatically in favor of doing field trials, but the report is clear-eyed about what they’re going to cost. Small-scale trials (less than 100 km², two months of observation) could run $3 to $25 million. A comprehensive program with multiple large-scale trials might come in at $250 million over ten years. For reference, the ExOIS consortium’s proposed northeast Pacific GOFOIF trial—currently the most advanced field trial concept—carries a price tag of $40 to $45 million for two trials over three years.

The pathway-specific priorities focus on sharpening the scalability picture for GOFOIF through realistic deployment scenarios (not idealized models), but also advancing the still-nascent science of subtropical nitrogen-fixation-based iron fertilization (building on the Tonga-Kermadec hydrothermal vent observations I’ve written about before), as well as funding early-stage innovation in export enhancement—clay flocculation, mineral ballasting, aluminum-based degradation resistance.

The implementation priorities are where the report earns its institutional credibility. Community co-design isn’t an afterthought—it’s baked into the stage-gate progression. Coastal community and fisheries capacity-building gets its own dedicated priority. And the report insists that PCS risks be contextualized against the alternative: doing nothing in a world where ocean primary production is already declining under climate stress.

It’s exciting to see people who command the respect of big-time funders thinking through these ideas in this way. This feels like the way you shift the whole concept from neat-in-theory to real-thing-we’re-going-to-do.

Still, though, if you’ve been tracking this space, you might ask: what does this add to the 2022 NASEM report or the ExOIS roadmap?

Three things, I’d say.

First, scope. By defining the PCS umbrella broadly enough to include export-based innovations alongside production-based fertilization, the framework opens up a richer design space for research. If the big problem with iron fertilization is that you can grow blooms but can’t reliably get the carbon to sink deep enough, then export enhancement can’t stay an afterthought.

Second, structure. The stage-gate approach provides something that previous roadmaps lacked: a clear, repeatable decision framework with explicit criteria for advancing, pausing, or killing a pathway. This is the kind of tool funders need to make defensible allocation decisions in a field full of uncertainty.

Third, realism about money. The report is designed for a world where PCS funding is scarce—starting with $1-5 million for initial sensitivity analyses and model improvements, scaling to $5-10 million for parallel pathway investigations and community engagement, building toward the $40+ million needed for large-scale field trials. If some random guy with a substack tells you that, that’s one thing. When the body set up by the biggest climate funders says it, it’s quite another.

That freeze is thawing. The NASEM report in 2022 gave scientific legitimacy back to the question. ORCA and the Grantham Trust put real money behind it. ExOIS started designing actual trials. Growing Oceans launched to study nitrogen-fixation pathways. And now Ocean Visions has produced the strategic architecture to coordinate the whole sector.

None of this means phytoplankton carbon is going to be a killer solution. The report levels with us about the possibility that it might just won’t work: uncertainties might prove irreducible, environmental risks might prove unacceptable, the math might simply not add up at scale. Those are legitimate outcomes of a well-designed research program: if we were sure it would work, there’d be no point to doing research.

But here’s the thing. We need 10 gigatons of CDR per year by 2050. We’re nowhere close. No other CDR approach combines scalability with affordability like phytoplankton does. The idea that we can afford not to rigorously investigate the ocean’s biological carbon pump—the planet’s largest natural carbon sequestration system—has always been more about politics than science.

The grownups are finally acting like it.

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The year is 2038.

You’re looking at a screen showing a patch of ocean 170 kilometers northeast of the Seychelles.

It’s the subtropical Indian Ocean gyre, some of the most nutrient-poor waters anywhere. Satellite data shows chlorophyll concentrations barely above detection limits — nothing’s growing there.

Your job is to operate a prescriptive ocean AI trained on reams of ocean data called Ocean Intelligence, OI to friend. The system has just identified a nearby patch with low iron, low fixed nitrogen, and fertilization assets close enough to be deployed in time. It flags the patch as the optimal deployment opportunity for carbon drawdown.

OI pulls together satellite observations, historical measurements from research cruises that have passed through this region to generate a set probabilistic projections about what happens if you intervene. It runs a full physics-based simulation of the next two weeks of ocean circulation in this exact patch, generating an ensemble of scenarios, each with a likelihood estimate. A mesoscale eddy is likely to develop, which could contain any bloom to a manageable area. Iron added now will hit a sweet spot—enough mixing to distribute nutrients, not so much that the bloom gets dispersed before carbon export begins.

The OI packages all of this into a recommendation. It specifies the intervention: three autonomous surface vehicles should deploy 12 tons of iron across 400 square kilometers in a specific geometric pattern.

It lays out the monitoring strategy: two underwater gliders positioned to track bloom development, a fixed mooring to measure CO₂ drawdown, satellite overpasses coordinated with profiling floats to measure particle flux. It estimates 200,000 tons of CO₂ sequestered with an uncertainty range of 150,000-280,000 tons. It flags potential risks: a 15% chance the eddy doesn’t develop as predicted, a 5% chance of unusual oxygen depletion based on similar historical cases.

But that’s just the oceanography. Next it has to deal with the bureaucracy.

This patch of ocean sits in the Seychelles’ Exclusive Economic Zone. You can’t just put iron in someone else’s waters because some computer says it’s a good idea. The OI generates an Environmental Impact Assessment formatted to the regulatory standards required by the Seychelles. It documents baseline conditions, projects ecological changes, quantifies likely impacts on fisheries and marine ecosystems. It shows that iron concentrations will remain below natural variability from dust deposition, that the intervention is time-limited and reversible, that monitoring will detect any adverse effects early. It compiles the whole package —data, methodology, risk assessment, monitoring protocols— and submits it to the Ministry of Fisheries. Then it waits for regulatory approval, just like any other marine research project.

But the OI is also about thinking economically. It pulls current carbon credit prices from compliance and voluntary markets, calculates the costs of deployment and monitoring, and builds a profit-and-loss model for this specific intervention. It estimates return on investment, but crucially, it doesn’t just show a single number. It shows the full distribution of possible outcomes—best case, worst case, most likely case—all couched in terms of quantified uncertainty.

Then it waits.

A team of oceanographers reviews the recommendation. They work for a non-profit run by scientists to operate the OI platform. They drill down into the physics model outputs, check the uncertainty bounds, examine the historical analogs the model used. For sure, they have questions: Why this specific iron dosage? What happens if the eddy arrives six hours early?

The Ocean Intelligence model is not itself a full physics-based ocean model, but it can always invoke one in high stakes situations. In this case, the OI runs several high-resolution physics-based simulations to answer the human team’s questions and presents its conclusions. After human review and regulatory approval, the oceanographers authorize the deployment.

The three wave gliders converge on the target coordinates and begin their runs, so monitoring begins immediately. Gliders descend and surface, transmitting data. The mooring records CO₂ changes. The OI checks them against satellite data monitoring chlorophyl and temperature and processes everything in near-real-time, continuously updating its predictions against observations.

Four days in, chlorophyll concentrations begin to rise. The bloom is developing exactly as predicted. But on day six, something unexpected happens: dissolved oxygen levels start dropping faster than the model had anticipated. The OI flags it immediately, runs diagnostics, determines it’s likely due to more intense bacterial respiration than the initial model suggested. It checks for harmful algal bloom species, for unusual changes in zooplankton communities, for any sign this is heading somewhere problematic.

The OI sends an alert to the oversight team, adding the regulators in the Seychelles in CC: “Oxygen anomaly detected, likely within normal bloom dynamics but 20% more intense than predicted. Recommend continued monitoring, no intervention suspension required.”

It runs the full physics-based model a dozen times to ensure its expectations are met. It shows its work—the results of the full physics-based model runs, its diagnostics, and comparison to historical blooms. The oceanographers and regulators concur. The operation continues. The OI adjusts itself in light of what it has learned from this experience.

By day fourteen, the bloom begins to dissipate. The profiling floats show particulate organic carbon sinking past 200 meters, past 500 meters. The OI then calculates final results: 220,000 tons of CO₂ sequestered for at least one century, verified by multiple independent field measurements, with a full counterfactual baseline, and backed also by several runs of the full physics model.

The OI packages everything into a verification report—raw data, model outputs, uncertainty quantification, counterfactual analysis—and hands it off to an independent verification team. They have their own physics-grounded AI, trained independently and using different methods to cross-check the results. The verification AI reviews the monitoring data, runs its own physics models, and confirms the carbon accounting. If the numbers match within acceptable uncertainty bounds, carbon credits get issued.

The credits hit the market, buyers pay up and apply them to the offsets to their own nationally mandated caps. Revenue flows back to fund the next deployment, with royalties also flowing to the treasury of the Seychelles. It’s their ocean, after all.

At each step, the OI learns from the experience: bacterial respiration parameters for this region need adjustment. The next recommendation will be more accurate.

That’s the vision, anyway. Whether it becomes reality depends on choices we make now.

To be clear, all the tech to build what I’ve just described exists today — it just hasn’t been integrated into a single tool. Using 2026 technology, building such tool would be complex but doable, if properly resourced. And AI technology is advancing enormously fast. Every year the barriers to building a tool like this will become less daunting. As the frontier pushes towards artificial general intelligence, tools like this that scan as futuristic today may come to seem almost humdrum.

I think when we look back, 25 years from now, we’ll wonder that anyone ever thought it would be possible to get on top of climate change without an AI-based prescriptive ocean model like this.

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If you saw the 2016 documentary AlphaGo, you remember Move 37. DeepMind’s fantastically sophisticated AI algorithm is playing against Lee Sedol, South Korea’s top Go player. The game looks “normal” until the machine does something that looks completely insane. You can hear the collective intake of breath from the professional commentators, the initial confusion after Move 37 —that can’t be right!— followed by slow, dawning recognition that something unprecedented is happening. Move 37 isn’t just bizarre, it’s superhuman. It turns the whole game. Lee Sedol eventually resigns.

Move 37 obsesses a certain breed of techie because it shows AI coming up with an idea no human being would even have considered. An idea so obviously “bad”, it merits no serious interest from a professional.

Go is hugely complex. On each turn, a player has hundreds of legal moves to choose from, and the opponent has hundreds of possible moves in reply. The decision trees that result are insane: just three moves out, there are hundreds of millions of possible board configurations. No one can hold that many possibilities in their mind at once, so human champions adapt by focusing their attention on just a handful of candidate moves that, after years of practice, they’ve learned to intuit as good. The vast bulk of possible moves, they discard without thinking about them.

This is how all human expertise works. To be an expert means to have a gut level feel for what’s likely to work. It means developing sophisticated pattern recognition that instantly eliminates the vast majority of possibilities, leaving a manageable handful open to consideration.

These pruning heuristics are what make human expertise possible.

But they also make certain solutions invisible.

AlphaGo beat Lee Sedol because it pruned the game tree differently. Not because it searched the entire thing — not even a computer can do that. Its neural networks, trained on millions of games and refined through self-play, had developed pattern recognition from different foundations. It hadn’t inherited human heuristics about shape and territory and influence. It learned directly from outcomes: positions that lead to winning.

When ocean biogeochemists think about marine Carbon Dioxide Removal, they face a pruning problem that makes Go look like child’s play.

Consider what’s actually involved in evaluating a potential ocean carbon removal intervention. Three-dimensional circulation patterns that vary seasonally and interannually. Biogeochemical cycles—carbon, nitrogen, phosphorus, iron, silica, others—each with their own dynamics and limitations. Microbial community responses. Temperature and pH effects on biological processes. Viruses. Potential downstream impacts on fisheries, on oxygen minimum zones, on atmospheric feedback loops.

The combinatorial space of possible interventions—location × timing × method × scale × duration × combination strategies—is utterly overwhelming.

Human ocean scientists have developed powerful pruning heuristics to navigate it. They focus on interventions they can measure exploiting mechanisms that fit their understanding of existing biogeochemical models on scales that match realistic funding constraints and available logistics. They mind their professional reputations, so they propose approaches that will seem “reasonable” to peer reviewers who’ve spent careers studying these systems.

These heuristics are earned. Built from decades of observations, failed experiments, hard-won theoretical understanding. They’re mostly correct. That’s why they persist, why they’re taught to graduate students, why they shape which proposals get funded.

“Mostly correct” means they also create systematic blind spots.

At Anthropocene, we support an approach to marine carbon dioxide removal that exploits a mechanism most research overlooks: extending the availability of bioavailable nitrogen in oligotrophic ocean systems by mimicking natural fertilization events. The specifics involve decision trees that make Go look like tic tac toe. How much of which nutrient do you consider, where exactly, in what form exactly, when exactly?

We have heuristics to answer these questions, sure, but they’re relatively blunt.

What would a Move 37 for nitrogen fixation for phytoplankton carbon look like? Impossible for humans to say. Maybe there’s some spatial patterns of intervention that exploits circulation in ways that seem geographically nonsensical until you see the global response. Maybe it’s a timing strategy that coordinate with seasonal dynamics in ways humans wouldn’t think to orchestrate, or some exotic cascade effect where small interventions in “unimportant” locations trigger disproportionate responses elsewhere, or some nutrient that bottlenecks a whole system that’s not on our radar. Who knows.

The best human Go player couldn’t have seen Move 37. The best human oceanographers probably can’t see the optimal approach to mCDR.

This is where physics-grounded AI becomes interesting.

I’m not talking about large language models that confabulate plausible-sounding nonsense, or pure machine learning approaches that need massive training datasets and can only interpolate within their training distribution.

I mean a world-model AI of the ocean. Imagine a neural networks training on synthetic data from GPU-accelerated ocean general circulation models with full biogeochemistry, constrained by conservation laws, grounded in thermodynamics. Training the neural network on physics model outputs could yield an emulator that runs orders of magnitude faster while still respecting thermodynamic constraints, making it possible to search intervention space at scale.

I’m increasingly convinced this is what mCDR research will look like in the next decade.

An Ocean AI system still wouldn’t be able to search every possibility: it still has to prune the decision-tree. But it eliminates possibilities for different reasons than human experts do.

The system would simulate millions of intervention scenarios, evaluating each against physical constraints—energy balance, nutrient budgets, circulation dynamics—without inheriting human preconceptions about what’s “worth trying.” It won’t know that certain approaches are “obviously wrong” by expert consensus. It would only know what the physics and the biogeochemistry allows.

The interventions that survive AI pruning but fail human pruning—that’s where Move 37 lives for marine carbon dioxide removal.

Building a GPU-accelerated ocean model with sufficient resolution and biogeochemical complexity is technically challenging but conceptually straightforward. The computational infrastructure exists, the physics is just a wall of Navier-Stokes equations—Newtonian physics in fluid dynamics terms. It’s a fully solvable engineering problem.

The hard part is what comes after.

When the model proposes an intervention that human experts have learned to prune away, then what do we do? Move 37 looked like a mistake to every professional Go player watching in real time. Several thought AlphaGo had just malfunctioned.

The ocean’s Move 37 will trigger the same response from marine scientists. At first.

This creates a bootstrapping problem. A physics-based AI system for ocean carbon removal needs to build credibility before anyone implements its most counterintuitive suggestions. It might start by proposing relatively conservative interventions—things that look plausible to human experts but that no one had specifically thought to try. Demonstrate that those work on the basis of physical measurements and you can gradually expand the envelope of what seems reasonable to test.

Of course, if the system only ever proposes things that feel safe to human intuition, we’ve wasted our time. We’d build it precisely because human pruning has blind spots. The credibility-building phase can’t become a permanent constraint. At some point, we need institutional capacity to take seriously—and actually test—interventions that violate expert heuristics but respect physics.

Thing is, this isn’t a problem that gets solved with better AI or more computational power. It’s institutional and cultural. We need funding mechanisms that can evaluate proposals outside the pre-pruned solution space. Peer review processes that can distinguish “this violates what we expect” from “this violates what we know.” Experimental designs that can test counterintuitive proposals from physics-based models while maintaining appropriate safeguards.

None of this means dismissing human expertise. Ocean scientists have built extraordinary understanding of these systems through patient observation and theory-building. That knowledge is what constrains the physics models, what validates their outputs, what identifies when simulations are producing artifacts rather than insights.

But expertise creates structure in how we search for solutions. And that structure has gaps.

Human-led incremental research is systematically exploring a pre-pruned solution space. That’s fine for building fundamental understanding of ocean systems—possibly optimal, even. It may not be good enough for finding gigaton-scale carbon removal solutions on climate-relevant timescales.

We’re at an inflection point where computational power has finally caught up to the complexity of the problem. GPU acceleration makes it possible to produce high-resolution synthetic training data from global ocean models at speeds that enable the resulting emulator to systematically explore the intervention space. The physics is well enough understood to constrain these models meaningfully, we’re not short of observational data to validate their behavior in unperturbed conditions.

What we don’t yet have is institutional infrastructure to take seriously what these models might reveal.

Physics-based AI for ocean carbon removal would serve multiple functions. High-precision verification and monitoring of interventions—tracking carbon flux changes, attributing them to specific actions, quantifying permanence and downstream effects. This capability alone would be hugely valuable, helping distinguish effective interventions from failed ones and building the empirical foundation for scaling what works.

But the real value proposition is discovery. Building a platform that can show us interventions we’ve learned not to see, by pruning possibility space according to physics rather than human intuition.

And then—this is the hard part—building the institutional capacity to actually try what that different pruning reveals.

The solutions we need for gigaton-scale carbon removal are almost surely sitting in the 95% of possibilities that expert pruning has learned to eliminate. Not because ocean scientists are wrong about what works. They’re probably mostly right.

Being “mostly” right means systematically missing the exceptions.

We’re still designing research programs for a world where human intuition is our only guide. That world ended with AlphaGo. The climate timeline doesn’t give us time to exhaustively search the 5% of intervention space that feels safe to human experts.

We need to search the other 95%—systematically, guided by thermodynamics rather than familiarity. The computational tools exist. The institutional capacity to trust them does not.

I wouldn’t be surprised if building that capacity turns out to be harder than building the models.

It’s also more urgent.

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Everybody knows oil is made of dinosaurs, right?

The idea is part of our cultural flotsam and jetsam, just a fact that enters your head and squats there. It’s a great image: there’s a reason oil companies, real and imagined, put it right there in their logos.

The truth, however, is less exciting.

Yes, the long hydrogen-and-carbon chains we get gasoline from really do come from long-dead organic matter. But almost none of it was charismatic megafauna. Mostly it’s plants: organisms that, millions of years ago, perfected the magic trick of soaking up energy from the sun and turning it into their own bodies. Most of that didn’t happen on land, most of it happened in the oceans.

In fact, the vast bulk of the old biomass that turned into oil was organisms you would need a microscope to notice: phytoplankton. Which just means “tiny marine plants.”

Most people live their whole lives never giving phytoplankton a second thought. When you start learning about them, you get obsessed. Microscopic plants were the dominant form of life on Earth for literally a billion years. They’re the reason the atmosphere has oxygen in it in the first place. For millions of years they drifted, soaked up solar energy, died, sank, and got buried. Over absurd geologic timescales, some portion of that biomass got cooked under heat and pressure into the hydrocarbons we now extract, refine, and burn.

Which means a tank of gasoline is condensed sunlight captured by ancient ocean life. The “carbon” in the “carbon emissions” everyone is worried about is just the long dead bodies of phytoplankton.

Maybe if people understood that their cars run on fossil phytoplankton, not dinosaurs, our climate conversation would make more sense. Because then they’d find it more intuitive that the trick to climate change is getting the carbon we’ve dumped into the atmosphere back to the state it spent the last several million years in: as dead organic matter in the ocean depths.

We can do this. Because the organisms that fossilized into oil have descendants still floating in today’s oceans. The phytoplankton of today aren’t identical to the ones that made the oil: they’ve had billions of years to evolve. But the basic gig is the same: use the energy from the sun to fix CO₂, build organic matter with it, die, then sink.

What we’re talking about is closing the loop: phytoplankton becomes gasoline. Gasoline becomes carbon dioxide. Carbon dioxide turns back into phytoplankton. Everyone goes home happy.

This, in fact, is what will eventually happen to if we give the ocean a few tens of thousands of years to do its thing. Trouble is, that’s not a pace that works for humans.

The problem is timing. The ocean carbon cycle isn’t one loop, it’s a loop with gears. Some parts spin fast: photosynthesis, respiration, seasonal blooms. Other parts move slow: deep circulation, sediment burial, rock weathering.

When humans burn fossil fuels, we’re taking carbon that nature locked up on the “millions-of-years” schedule and releasing it on the “Tuesday morning” schedule. Once you see the mismatch, you recognize the problem of climate change is “how do we match the speed of carbon removal to the speed of carbon release?”

Can we accelerate the part of the loop that pulls carbon back down? Can we work with nature so it does what it was going to do anyway, but quicker?

Because the biosphere already knows how to take CO₂ out of the air. It does that every day. We don’t need to genetically engineer some new organism to do this, nature did that work for us. We just have to feed them.

This isn’t science fiction. There are places where something like this appears to happen already. Near Tonga, undersea volcanic activity injects nutrients and trace metals into surface waters, stimulating phytoplankton growth—more photosynthesis, more biomass, more carbon drawn out of the surface system. Saharan dust does the same thing in the North Atlantic, a major reason it’s a better carbon sink than the other oceans. Even ash from forest fires can play this role.

Sometimes the ocean gets a boost. A fertilization event. A reminder that the biological pump isn’t fixed, it’s responsive. Turn the right knobs and the biology ramps up. So the question isn’t “can the ocean take up carbon?” We know it can. The question is: can we accelerate the rate safely and predictably, at scales that matter?

I think we can. Once you frame it appropriately, this seems like it’s obviously the best response to the climate crisis. Figuring out the how is what I spend all my time on.

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