Let’s just re-engineer the climate

Well, maybe not. Geo-engineering isn’t the easy and painless fix for climate change that many proponents say it is.


Harvard engineering professor David Keith is a big proponent of geo-engineering — using technology to save the planet from climate change. Maybe we’ll do some Solar Radiation Management (SRM) by injecting sulfate aerosols at high altitudes to “turn down the sun,” reducing the amount of its radiation hitting the Earth’s surface. Or we might instead find ways to suck the CO2 we’ve put into the atmosphere back out and pump it into the ground.

To be sure, Keith thinks that the first and most important thing we can do to tackle climate change is to reduce CO2 emissions, but he thinks it would be crazy to be against exploring these other options as “Plan B.” Indeed, he has an analogy:

Imagine a doctor refusing to administer chemotherapy to a stage III lung-cancer patient out of fear that it would reduce his incentive to cut his smoking habit from two packs to one pack a day. That, in a nutshell, is the morally obtuse thinking that has undermined humanity’s best bet to curb climate change: solar and carbon geo-engineering.

Morally obtuse? It’s certainly a powerful analogy. But is it the right one? I don’t think so.

Someone diagnosed with stage III lung cancer has — according to a few medical web sites I visited — a roughly 10% chance of living for another 5 years. There are treatments, and they’re getting better, but this condition is in most cases terminal. No matter what is done, the chance of surviving the cancer and going on with life is very, very low.

This is a terrible analogy to our climate situation, because, while our current emissions trajectory, is bad, there is every reason to believe that a determined global effort to reign in emissions and switch to cleaner (i.e. not CO2 emitting) energy could keep warming to less than 2 degrees C. The consequences of that would, scientists believe, be manageable, if not great. A better medical analogy for our climate predicament would be to a patient who is currently a very heavy smoker, deeply habituated to that health-damaging practice, and beginning to suffer from hacking and wheezing etc, but who doesn’t yet have cancer.

Indeed, Keith’s analogy would make more sense if the consequences of warming were already with us, catastrophic and irreversible, short of dramatic intervention in the climate system. It would be right if climate change had already brought to a halt the global system of oceanic currents which move heat and salt around the world. Or, if global average temperatures had already gone up by 5 degrees C, and were set to climb higher still. If we didn’t think seriously about geo-engineering then, that would be crazy.

But being hesitant about it right now isn’t crazy at all. Given the forces pushing back against CO2 reductions — big coal and oil, of course, well-funded conservative think tanks, and simple human nature, among them — it is completely unrealistic to think that wide discussion of the allegedly “simple fixes” offered by climate engineering won’t reduce the incentives for making the kinds of changes we need. Indeed, it will most likely become a major element of the rhetorical arsenal used to argue against the need for CO2 reductions.

More importantly, the idea that geo-engineering is a simple fix is deeply incorrect. Take Solar Radiation Management. Let’s say we spray lots of sulfate aerosols into the atmosphere, mimicking the effect of volcanic eruptions, which we know tend to reduce global temperatures. The aerosols reflect more sunlight back out into space. Proponents of the idea imply that we can, in this way, reverse the influence of CO2 and keep global temperatures from changing. We can go right on ahead burning fossil fuels. One potential problem is that we’ll have to keep pumping aerosols into the atmosphere indefinitely, and in increasing density, to counter the still increasing levels of CO2. The consequences of stopping — due to international disagreements or war, for example — would grow more dire with time, as we’d experience extremely rapid warming upon any cessation of aerosol injection.

So there’s really no sense in which this would be returning the atmosphere to its state before our activities put so much CO2 into it. We’d just have an atmosphere with even more CO2 and increasing levels of aerosols as well, even further removed from the atmosphere of a few centuries ago.

There’s also another reason SRM won’t take us back: it actually won’t even keep temperatures stable. As atmospheric scientist Anders Levermann points out, it will actually increase some forms of climate disruption:

The reason is as simple as fundamental: The extra abundance of greenhouse gases in the atmosphere does not change our climate in a uniform manner. The Arctic, for example, is warming almost twice as much as the tropics. This has to do with a well-known effect called polar amplification. The main reason for this is that warming enhances the amount of water vapor in the atmosphere, which then snows-off in the dry and cold polar region where it releases energy and warms the atmosphere. Now, if this sounds too complicated, one just has to hold up a thermometer in the Arctic and another one in the tropics: They show that temperature up North rises faster than at the equator.
Now, reflecting sunlight back into space would have the exact opposite pattern. It would do a lot in the tropics where sunlight is strong, and less in the Arctic and Antarctic. This is fundamentally true and cannot be fixed. So, reflecting radiation back into space could cool the planet on average, but it cannot reverse the effect of the greenhouse gases — not even remotely.

Again, this is not the story one often hears from fans of climate engineering. Keith suggests that it has the potential “to roll back — not just delay — carbon’s climate impacts,” but that isn’t the case. Driving a further increase in the temperature difference between the poles and equator isn’t going to do much to stop melting of ice sheets.

Removing CO2 would be a better option, but it’s not perfect either. Technologically, it’s hard to do . Maybe we can effectively replant all the trees and other vegetation which have been removed by human activity? Sounds good, but that will take time, and compete with agriculture. Maybe we’ll invent some super efficient way to remove CO2 using nanoelectronics; this recent paper reported a significant advance on that front. But even with great technology, the scale-up required for effective use will be tremendous. It would have to be done on a truly enormous scale — comparable to all the human activity currently putting CO2 into the air. We essentially need a second industrial revolution to counter the first one.

At which point you might think — maybe a revolution in economic organization and social habits to reduce CO2 emissions might be quite a bit easier.

In his recent essay, Keith expressed disappointment that geo-engineering still gets little attention in international climate negotiations. I think that’s OK. It may be something to consider if all else fails, when the consequences of climate are already as serious and irreversible as those of Stage III lung cancer, and there truly is no other option. Until then, of course, some limited research makes sense, so we know more about what we should expect from different means of intervention. To be honest, we ought to be learning much as we can abut climate and how it works no matter what. Even if we do solve the contemporary climate change problem, we may be challenged in other ways in future — from climate change that is rapid, unpredicted and not linked to human activity. It would be good to know as much as possible about how we might respond.

But for now, geo-engineering ought to remain far down the list of practical things to do about climate change.