The four things a climate strategy has to get right

Being scientifically sound is not enough

To be successful, a strategy to fight climate change has to meet four criteria. It must be:

1. Affordable at scale,

2. Timely,

3. Scientifically and technologically sound, and

4. Socially and politically acceptable

The bad news is that none of the approaches available to us today meet all four criteria.

Still, some are better than others. And the approach the climate movement spends almost all its energy on, alas, is not one of the better ones:

Reducing greenhouse gas emissions has been at the center of our climate debate since the 1990s, and you can see why. It’s greenhouse gas emissions that are causing the problem, it stands to reason we would look for a solution there first. Yet it won’t work, because it fails on the three other criteria.

With a price-tag in the tens of trillions of dollars, trying to curb climate change by reducing GHG emissions is patently unaffordable. Attempts to implement it work themselves out in the form of higher energy prices, making it politically toxic and losing its proponents elections all around the world.

Worst of all, even if we could reduce emissions quickly (which we can’t), the strategy can’t arrest global warming, much less reverse it: all it can do is slow the pace at which the planet goes to hell.

It is, in other words, a failed strategy.

If our climate conversation is stuck, it’s because we’ve yet to come to grips with the reality that no amount of feel-bad enviro-hectoring will make emissions reduction cheaper, or more politically palatable, or quicker.

It isn’t working, and it won’t work.

One of the costs of overcommitting to this emissions mitigation strategy too early is that it’s made us lose sight of other approaches, perversely turning better alternatives into taboo subjects.

The way out of the morass is to go back first principles, to go all the way back to the first page in the textbook and review the basics of how the earth’s energy balance is established to look for levers we can pull that meet as many of our four criteria as possible.

When we’re ready to do this, albedo will jump out at us at once. Because the earth’s energy balance is a function not just of how much energy the greenhouse effect locks in, but also of how much energy our atmosphere bounces back out to space. Scientists have known for decades that making the earth just one percent brighter would bring the earth’s temperature down to where it was in 1750.

Albedo —the proportion of solar energy the earth reflects back out to space, rather than absorbing— is the elephant in the room of our stuck climate conversation.

Two ideas for making the earth brighter seem to me to meet three of the four criteria above.

Brightening the stratosphere is the proposal most often discussed, and for good reason. The science is relatively straightforward, and all indications are that we could do it affordably and it would have an impact in months or years, not decades or centuries.

The problems with Stratospheric Aerosol Injection (God even the name sounds ominous) are all about public acceptability and, therefore, politically feasibility: however elegant the science may be, however much it might rub engineers’ erogenous zones, it’s fundamentally a call to pollute our way out of our pollution problem. Calls to inject weird chemicals into the atmosphere offend people. It’s never a good sign when a committed core of conspiracy theorists is convinced that the thing you’re proposing is already being done by shadowy cabal. Which is why I suspect that stratospheric aerosol injection has an insurmountable public opinion problem.

That's why I tend to focus more on marine cloud brightening, a proposal that requires putting into the atmosphere nothing scarier than the stuff you sprinkle on your eggs in the morning anyway. Salt, plain old sodium chloride, is just too familiar a substance to scare anyone. Salt doesn’t immediately strike us as a pollutant, just the opposite. In Japan, where I live, salt features prominently in many purification rituals: this is why you see shinto priests tossing salt around the Sumo rink before a bout starts.

I can just about imagine how you could create the messaging that brings public opinion, perhaps reluctantly, to accept the necessity of adding it to marine clouds to make them brighter.

The problem with cloud-based approaches is that a huge amount of the science for it is still to be worked out. Actually, when you start really reading about this stuff, you can’t help but be shocked by how little we really know about clouds. We know the broad outline, sure — we know they’re made of liquid water or frozen ice clumped around aerosols. But in order to launch a major program aimed at altering the earth’s energy balance, we’d need to understand aerosol cloud interactions in minute detail — and we don’t.

There are many different kinds of clouds, many different types of aerosols which come in many different sizes, and there’s an immense variety of meteorological conditions in which they come together. We have only the vaguest notion of how any one aerosol interacts with any given type of cloud in a given atmospheric condition.

We have good theoretical reasons to think adding nano-scale salt particles to certain types of marine clouds would make them brighter, which could help cool the planet. But beyond that, the list of answered questions is daunting.

How much salt do you need to achieve how much brightening? In what atmospheric conditions would this work better, and in what conditions will it work less well? Will these brighter clouds tend to produce less rain than duller ones? How will they affect large scale circulation patterns? Are there enough clouds susceptible to brightening to make a difference to global temperature? Can cloud brightening be used selectively, to cool just one region — to suppress hurricane formation in the Atlantic, for instance, or to protect the Great barrier reef? What will brighter clouds do to large scale atmospheric circulation patterns? How will they impact coastal and marine ecosystems?

And beyond all those questions —all crucial, all still sort of up in the air— there’s another set of questions at a higher level of abstraction that is just as important and just as unsettled: how do you write a computer model that can capture all these interactions well enough to serve as the basis for a full-fledged marine cloud brightening proposal?

Even if we had a detailed understanding of the microphysics of aerosol-cloud interactions (which we don’t), until we’re able to recreate them in a climate model we can’t possibly know how to exploit clouds to cool the planet.

Plenty of climate repair advocates see this unending list of things we don’t know about aerosol cloud interactions and throw their hands up in despair. There’s a tendency to see clouds as too finicky and evanescent to work with: an inscrutable mystery floating overhead. I call that defeatist. It’s obviously a devil of a scientific challenge, but we’ve solved harder problems than this in the past.

There’s no doubt that it will take a lot of research and a lot of money to answer enough of these questions to bring Marine Cloud Brightening from the realm of speculative science to the realm of practical proposal. There are many different hurdles at which the proposal could fall. One researcher I talked to tells me her suspicion is that there just aren’t enough susceptible clouds out there to shave more than maybe 0.5 degrees celsius off of global temperatures by brightening them. Others suspect the hydrological effects will doom it: maybe you can use clouds to blunt climate change, but if that stops the rains over the Amazon, it’s a non-starter. It may yet be that the proposal is too risky, or too uncertain ever to put into action. But it would be madness to declare it so now.

If I had to guess, I would guess that by 2050 or so we’re going to be pursuing a combination of at least three of the techniques in my little Venn diagram above. Greenhouse gas emission reduction is inescapable, and I’m sure we’ll have much more carbon-free energy by then, but I don’t for a moment believe that’ll be our only strategy. We’ll certainly be at least trialing stratospheric brightening, even if I’m sure many greens will lose their minds about that. If the science on marine cloud brightening has panned out, we’ll be actively brightening marine clouds and probably at least experimenting with ocean fertilization and alkalinization. We may have made some sort of breakthrough that allows us to capture carbon directly from the air at scale, though this seems to me unlikely. It’s even imaginable, just, that we’ll find ways to try some of the crazier things, like mirrors in space.

I’ll tell you what we won’t be doing, though: we won’t keep the discussion confined narrowly to decarbonization. That strategy has already failed, and its corpse won’t come back to life just because we’ve neglected to bury it.