Among climate scientists, Ken Caldeira is a self-described troublemaker.
For instance, in a research paper delivered to the American Geophysical Union in December 2005, Caldeira annoyed tree-huggers and corporations alike by demonstrating that planting trees in most locations around the world actually exacerbates global warming. Although trees absorb carbon, their dark leaves absorb heat that otherwise would be reflected into space.
“We like to be troublemakers and do simulations that come up with answers people don’t like,” Caldeira says.
Indeed, one such set of simulations produced results that Caldeira himself didn’t like. Specifically, climate models developed at the Carnegie Institution’s Global Ecology Department on the campus of Stanford University—where Caldeira serves as staff scientist—showed controversial “geoengineering” ideas effectively would counteract the effects of global warming, without major adverse side effects (see sidebar, “Pulling the Shades on Global Warming” ). Public Utilities Fortnightly caught up with Caldeira recently to discuss his perspectives on geoengineering and its possible role in strategies to address climate change.
Fortnightly: What’s your perspective on geoengineering ideas such as those proposed by Edwin Teller, Freeman Dyson, and Roger Angel? Are these ideas as wacky as they seem?
Caldeira: They range from very wacky to less wacky. The wackiest ones involve putting shields in space, a million miles away, between the Earth and the sun. What’s not so wacky is putting tiny particles, namely sulfates, into the stratosphere.
Fortnightly: I would’ve thought the space-shield idea was less risky than the idea of polluting the atmosphere with sulfur. After all, we’ve been trying to reduce SO2 emissions for 30 years.
Caldeira: It’s an economic issue. Carbon capture and storage technology, according to the IPCC [Intergovernmental Panel on Climate Change], might cost about $30 per ton of carbon. To achieve the equivalent cooling with spacecraft would require blocking roughly a square meter of sunlight 1 million miles out, per ton of carbon. Assuming it’s even possible on the huge scale needed, the idea that you’d be able to do it for less than $30 a square yard is far fetched and wacky.
But putting about 100 cubic meters of sulfate or other tiny particles into the stratosphere would deflect enough sunlight to compensate for doubling the natural levels of CO2, and you could keep that much stuff up there for a couple billion dollars a year.
Fortnightly: What about acid rain?
Caldeira: It turns out if you put sulfur into the stratosphere, it stays there potentially for years, whereas in the lower atmosphere—where smokestacks put it—the sulfur rains out in a couple of days. And the amount you’d put into the stratosphere is actually much less than we are putting into the lower atmosphere today.
I’ve done a bunch of climate model simulations looking at how effective these schemes would be. I’m philosophically opposed to all of them, because if you go down the path of interfering with the climate you might damage the planet in ways you can’t fix. But our model simulations indicate these schemes would work quite well to reverse the effects of global warming, and nothing terrible would happen.
Of course the climate is a lot more complicated than what is represented in models, and nobody really knows what would happen.
Fortnightly: What are the biggest risks of this approach?
Caldeira: There are concerns about what it would do to ozone chemistry. Would it end up destroying the ozone layer? Scientists and models say it won’t, but nobody predicted the ozone hole over Antarctica before it appeared either.
One problem would be ocean acidification, from the ocean absorbing CO2 and killing coral reefs and other species. Geoengineering won’t solve that problem.
Some people suggest blocking sunlight will hurt agriculture, but our simulations indicate, on balance, sunlight that is more diffuse combined with increased CO2 would make the biosphere grow more vigorously.
I would feel happier if our simulations suggested some clear reason that geoengineering is a terrible idea, but no real show stoppers have presented themselves.
Fortnightly: These ideas have received attention recently, but historically they’ve been considered too speculative and grandiose to be taken seriously. Is that changing, or is this still the stuff of science fiction?
Caldeira: It’s a little beyond sci-fi. People who are pretty savvy from a policy point of view are at least discussing it. There’s still no funding for it, probably because it is considered too politically dangerous for anyone to touch it. But in backrooms more serious people are thinking sooner or later we will end up deploying these schemes.
In November 2006 we convened a meeting at the NASA Ames Research Center [Editor’s note: This was a closed-door meeting] that included many luminaries, including Nobel Laureate Tom Schelling. He and others are getting a sense of despair that we will ever a-chieve international coordination on the level necessary to reverse climate change.
I compare it to the Iraqi oil-for-food program. How are you going to actually police a carbon-capture and storage regime? When you start thinking about how you actually solve these problems, it would be very attractive if we had a quick technology solution like geoengineering, which doesn’t need international agreements but can be done by one country, and is economically feasible and effective according to the climate models. On that basis it is a realistic proposition.
Fortnightly: What about the argument that geoengineering is a distraction that will hinder efforts to address the root causes of global warming?
Caldeira: I don’t see a whole lot of political momentum toward seriously addressing the problem, just a lot of superficial things that will be ineffective. That’s because politicians have a lot to gain from appearing to address it, but little to gain from actually solving what is a multi-decade problem.
One scenario is that we won’t really do anything until a catastrophe happens, and then people will demand that we do both [transition away from fossil fuels and conduct geoengineering]. When the s--- really hits the fan— when huge droughts in the Midwestern breadbasket are collapsing our agriculture system, ice sheets are melting, sea levels are rising, and we’re getting hit by Katrina-scale hurricanes—geoengineering might be an emergency back-up system we could deploy.
We should avoid geoengineering if possible, but we need it in our toolbox in case of catastrophe.