Or we could store all the extra CO₂ at the bottom of the ocean

Why settle for repairing the climate when you could restore it to its 1750 state?

AI slop courtesy of ImageFX

As an enthusiast for albedo-based climate repair techniques like Marine Cloud Brightening and Stratospheric Aerosol Injection, I’ve seen my fair share of silly, disingenuous and just plain absurd criticisms. But there are also a couple of serious objections. The strongest one is the argument that by cooling the earth without lowering CO₂ concentrations in the atmosphere, albedo-based techniques manage only the symptoms of climate change, but don’t address the underlying causes.

Surely, critics say, it would be much better to pull all the extra CO₂ out of the air altogether.

As it turns out, this is perfectly doable. It’d be cheap. We could do it with technology that already exists. We’ve tested it and it works.

Welcome to the world of Ocean Iron Fertilization.

The idea is to find ocean “dead-zones” —patches with little marine life— and spray them with trace amounts of iron to increase the number of phytoplankton (basically microscopic seaweed) there.

Why? Because even though phytoplankton account for a shockingly large portion of the photosynthesis on the planet (about as much as all the land-based plants put together), large parts of the ocean seem to host almost no phytoplankton at all.

Oceanographers spent decades arguing about why that is. In the 1980s, a researcher by the name of John Martin of San José State University proposed that the problem was iron deficiency. Phytoplankton need trace quantities of iron to grow and reproduce. Near the coast, dust blowing from land brings iron with it and fertilizes the waters naturally. Farther from land, large swathes of the ocean just don’t get any iron at all, meaning they can’t sustain phytoplankton.

The upshot, Martin realized, was that adding small quantites of iron to the surface of iron-deficient waters could result in startling jumps in phytoplankton numbers. From there, the math is simple: the more of phytoplankton there are in the ocean, the less CO₂ there is out in the atmosphere.

Think of it the marine equivalent of tree-planting — only instead of planting millions of trees, you’d be “planting” trillions of microscopic seaweeds: tiny organisms that eat CO₂, die, sink to the bottom of the ocean and lock it away there.

Ocean iron fertilization has a lot going for it. For one, you don’t need to use any land since, duh, you’re in the ocean. And just like planting trees creates habitats for lots of other life forms, fertilizing phytoplankton creates a food source for everything else in the water, from zooplankton to krill to fish to whales.

Not all of the CO₂ that phytoplankton absorb through photosynthesis will end up safely locked away in the bottom of the sea, but some portion of it will. Nailing down precisely how much is still a subject of research, but even the part that isn’t permanently locked away in the bottom of the sea will stay out of the atmosphere for some time.

What’s alluring about this idea is how simple and just plain low-tech it is. The key input, iron sulfate, is already a feedstock in commonly-used farm fertilizers: we’ve been producing it on an industrial scale for a hundred years. It’s cheap. It’s not toxic. Pretty much any sea-worthy ship with any old nozzle would do for a delivery mechanism. We’re at the opposite end of the spectrum from climate repair as futuristic sci-fi geek stuff.

So why isn’t this happening already? Because, alas, the conversation on CO₂ removal is, somehow, even more broken than the one about albedo-based climate repair.

Tech bros got hold of the idea of Direct Air Capture and immediately set about the task of proposing monstrously expensive and complicated engineering solutions to suck CO₂ out of the air that look shiny in a powerpoint presentation and make them sound virtuous at dinner parties, but definitely won’t scale. DAC now “owns” the conversation around CO₂ removal. Should it?

If we subjected our green initiatives to the kind of scrutiny we subject our altruism to, we’d see it shouldn’t. If we took Effective Environmentalism as a banner and subjected techniques to even rudimentary cost-benefit analysis, we’d see it’s not much of a contest.

According to this 2022 National Academies of Science report, you can sequester a ton of CO₂ with about 40 cents worth of iron. Direct Air Capture now costs in the order of hundreds to low-thousands of dollars per ton. Iron, then, starts with a three order-of-magnitude cost advantage.

That means that removing, say, 50 gigatons of excess CO₂ would cost in the order of tens of trillions of dollars with DAC machines, doing it with iron fertilization would cost something in the tens of billions. That’s the difference between the GDP of the U.S. and the GDP of Albania. Or the difference between something actually achievable and an idle pipe-dream.

The real draw of OIF is that it wouldn’t just mask climate change, it would reverse it. Ocean fertilization is the one technique I’ve heard of that could actually restore a pre-industrial level of greenhouse gases at a cost that we could realistically afford, and without any heroic assumptions about new scientific discovery or technological breakthroughs.

Of course, the technique remains controversial because, well, because some “green” groups seem more interested in fighting capitalism than fighting climate change. And yes, more research would certainly be needed to rule out unforeseen negative consequences, as well as to optimize all the details —how much iron? where? when? in what form? how often? in what ocean and atmospheric conditions?— as well as to better measure how much of the CO₂ absorbed does in fact get permanently sequestered.

What’s needed first is a sense of urgency to get these trials going. As Peter Fiekowsky notes, without some kind of large scale carbon removal strategy we’re stuck with permanently elevated carbon dioxide levels for centuries to come. Which means we will eventually have to take a serious look at techniques like this one.

And, well, time’s a’wastin’…