By David Keith
It’s not about implementing a scheme to cool the planet tomorrow—it’s about giving future generations the information they need to make a smart choice.
Solar geoengineering is not a quick fix for climate change.
Solar geoengineering is the idea that humans might deliberately increase Earth’s reflectivity, perhaps by putting reflective aerosols, such as diamond dust or fine droplets of sulfuric acid, into the stratosphere as a means to temporarily and imperfectly offset some of the risks of accumulating greenhouse gases.
But it is not a substitute for cutting emissions—it is a supplement. It could greatly reduce risks over the next century in ways that cannot be achieved by any reduction in emissions. Regardless, we can’t keep using the atmosphere as a free waste dump for carbon and expect to have a good climate no matter what we do to reflect away small amounts of sunlight.
A combination of cutting emissions and solar geoengineering could get us with near certainty to a world in which the amount of warming (the increase in average temperature) is less in 2100 than it is today. Emissions cuts alone cannot achieve this with confidence, because even if we completely stop emissions tomorrow, the inertia of the carbon-climate system will continue to warm the world for years. For instance, if the current warming causes permafrost to release its carbon—just one of the many carbon cycle feedbacks—then warming in 2100 could easily be about the same as warming today or even slightly worse even if we cut emissions to zero tomorrow. By cooling the planet, solar geoengineering can slow those carbon cycle feedbacks, reducing the cumulative carbon and thus reducing ocean acidification.
With a combination of solar geoengineering and emissions cuts, we could be confident of avoiding the 2 degrees Celsius of warming that, although somewhat arbitrary, is widely seen as a threshold of dangerous climate change.
Early use of solar geoengineering could allow us to preserve some Alpine glaciers and Arctic ecosystems that will be lost under any reasonable scenario for emissions control. For what it’s worth, these are places I know and love well—they are among the reasons why I have worked near the interface between climate science, energy technology, and public policy for 25 years
Because the warming impact of carbon is more or less forever, all that we can achieve this century by cutting emissions is to stop making the problem worse. Solar geoengineering allows a more optimistic outcome. In combination with technologies to remove carbon that is already in the atmosphere, it would allow humanity to aim to restore the preindustrial climate over two human lifetimes.
Despite this promise, there is little organized research on solar geoengineering. The U.S. National Academy of Sciences highlighted the potential of solar geoengineering in 1982. It delved deeper in 1990 and again in January 2015, when it recommended a broad research program and suggested that small-scale outdoor experiments could yield valuable knowledge.
Yet there is still no U.S. government research program. There are now research programs in China and a handful in Europe, but they focus on social science—governance, risk, and ethics. These are important questions, but none are focused on ways to improve the technology’s efficacy or reduce its risk. The worldwide effort on finding better, safer ways to do solar geoengineering probably amounts to fewer than the equivalent of five full-time people.
The overriding concern has been that even talking about solar geoengineering will raise the prospect of a quick fix, impeding efforts to cut emissions. I believe this fear has led many scientists to systematically understate the potential efficacy of solar geoengineering because of political concerns about its potential misuse. To be clear, this is a real problem that should not be underestimated. But in a democracy, it should not be the scientific elite that decides policy. The job assigned to scientists is to explain the facts as best as they know them and to (separately) explain their views about ethics and politics.
The ethical case for restricting research on solar geoengineering because of its potential misuse is at best ambiguous. First, the question of how people and governments react to a risky Band-Aid technology is an empirical matter. Good theories point in both directions. It’s largely a matter of how solar geoengineering is discussed, not whether. There are plenty of ways that solar geoengineering could help lubricate rather than frustrate emissions cuts.
Second, the people most likely to benefit from its use are mostly among the world’s most vulnerable or are yet to be born. We need to develop institutions that enable democratic debates on the use of these technologies not to close this debate down prematurely.
Perhaps I have convinced a few of you that we should go out and do solar geoengineering. If so, I owe you an apology. It would be irresponsible—maybe crazy—to just start now, even in conjunction with significant emissions reductions.
Yes, there are hundreds of scientific papers, but most simply apply climate models to simplistic scenarios for injecting sulfates into the stratosphere. There is no serious plan for implementation, no adequate plan for monitoring. The world lacks even a rough agreement about how to make decisions about how much geoengineering to do. There is no focused effort to develop better—lower-risk—technologies, nor is there a focused effort to build a deep technical critique of the ways that the implementation plan—the one with don’t have—could go wrong.
Perhaps you are already convinced that solar geoengineering is an idea we should abandon for good. Whatever you or I think, however, the next generation will be faced with the decision to implement these technologies. They cannot be un-invented.
If we have no research program, then we give our children the gift of ignorance. If climate change is worse that we expect, they will have to make decisions about geoengineering on that basis.
What is needed is a diverse systematic effort to understand how solar geoengineering might work. The research program must be noncommercial, open-access, and internationalized. It should look for ways to reduce the risks by improving the technology and to take systematic steps to understand how it might be effectively governed. It also needs to look at all the ways that solar geoengineering can go wrong.
But look we must.
David Keith is professor of applied physics in Harvard’s School of Engineering and Applied Sciences and professor of public policy in the Harvard Kennedy School. He also helps lead Carbon Engineering, a company developing technology to capture of CO2 from ambient air.
Published by Slate on January 19th, 2016.
