Technology to Cool the Planet: An Interview with David Keith

For twenty years, Harvard professor David Keith has worked near the interface between climate science, technology, and policy. In his new book, Keith makes the argument for climate engineering, a technology that cools the planet by spraying sulfate aerosols into the atmosphere. The particles then reflect sunlight back into space, reducing the amount of sunlight that hits the earth. Opponents to climate engineering argue that humans should not interfere more; Keith believes we have been interfering for thousands of years. 

Join us for a discussion about climate engineering with David Keith, Kenneth Oye, and Stephen Van Evera on Wednesday, October 30 at MIT. It is free and open to the public. More details here. 

Boston Review: First, can you explain to readers why sulfates are good candidates for geoengineering, as opposed to other molecules?

David Keith: Sulfates are the devil we know. Small water droplets would be roughly as effective as sulfuric acid in reflecting sunlight—clouds, composed of water droplets, are white and reflective—but they would evaporate almost instantly in the dry air of the stratosphere. The sulfuric acid keeps the water from evaporating.

Sulfur emissions from fossil fuel combustion are already cooling the planet and killing roughly a million people a year from air pollution worldwide. The amount of sulfur that would need to be put in the stratosphere for solar geoengineering would be a few percent of current fossil fuel emissions. Any such injection would carry real environmental risks such as ozone destruction and acid rain, but sulfates have the advantage of being a common atmospheric chemical, one that is injected into the stratosphere by volcanic eruptions. So although sulfates are risky, we have some empirical evidence about what the risks are.

BR: But why not just reduce emissions? Are we giving up on that when we do geoengineering?

DK: Geoengineering without emissions reductions just digs a deeper hole. Emissions reductions are a necessary part of any sensible climate policy.

It is possible to make big progress cutting emissions if we implement policies that include a significant price on carbon emissions and strong incentives for clean energy innovation. But while it is in our power to end the phony war on carbon and begin serious work to drive emissions toward zero, it would be extraordinarily hard to bring emissions near to zero in less than half a century, and even if we did, substantial climate risk would remain from the carbon that has accumulated in the atmosphere, carbon that will keep changing the climate for centuries to come.

Solar geoengineering provides a means—risky and uncertain—to limit climate change in the near term, risks that fall on vulnerable ecosystems and vulnerable human populations. But solar geoengineering can do nothing to limit the very long-term risks associated with carbon buildup in the atmosphere. Thus there is a sense in which emissions reductions and solar geoengineering are complementary.

BR: Among lay people, geoengineering is seen as a pretty fringe, even dangerous, idea: how do others in the scientific community view it?

DK: There been several efforts to do systematic polling for public opinion on solar geoengineering, and a few efforts, one just nearing completion by my student Ashley Mercer, to examine expert judgments. My takeaway from an early look at this data is that expert and lay judgments are surprisingly similar. Both groups show acute—and sensible—concern for the risks and are deeply concerned about implementation, and both show significant support for further research.

BR: One thing your book makes clear is the difference between technical limitations and policy limitations to geoengineering: while the technical limitations are pretty small, and policy limitations pose huge challenges to both research and implementation. On the other hand, policy limitations end up being important for preventing hasty action. How should this dynamic work, ideally?

DK: That’s a near-impossible question. I suppose if I had one vain wish, it would be that debates about facts and values could be more clearly separated. There are sound reasons to oppose or support geoengineering, but both opponents and proponents too often deliberately misinterpret the science to bolster their respective cases. The public debate would be better served if both sides made policy arguments on their intrinsic merits rather than trying to avoid the hard policy and value-focused arguments by simply asserting a set of facts that seem to prove their case beyond doubt.

BR: I think a lot of people have the idea that climate engineering is primarily geared toward counteraction and prevention—in other words, erasing the human footprint. You point out that human presence has been changing the environment for thousands of years, and likewise that geoengineering can’t return us to a previous state, but potentially has several ends. The implementation of climate engineering could be calibrated to promote crop growth or preserve the poles, for instance. How mutually exclusive are these goals?

DK: The goals are—in many cases—mutually exclusive. You could use solar geoengineering as part of an effort to limit the environmental footprint of humanity or use the same technology to reshape the earth to suit human wishes—but you cannot do both at once. My vote is that this generation focuses on limiting our footprint.

BR: You talk about how an economic and utilitarian framing of climate change (e.g., investing money in climate now will save us later) is unconvincing, but throughout the book, the language of risk assessment is used to question the benefits of various types of engineering. What can we learn from cost-benefit analysis, and what are its problems? To what extent does our approach need to be focused on reducing emissions, and to what extent does it need to be realistic about the prospects of actually doing so?

DK: Cost-benefit analysis is a great tool for making trade-offs between similar things; it’s a necessary tool, for example, in doing a better job of allocating healthcare funding effectively in the United States. It becomes less useful when you are comparing widely different outcomes such as the cost of cutting emissions today versus climate impacts for our unborn great-grandchildren, or the value of spending healthcare dollars in America compared to spending dollars in Malawi. As I say in the book, “Paraphrasing Churchill, one might say that this utilitarian stance is the most unsatisfying basis for public policy except for all the others.”

BR: One of the things you combat in this book, from the inside, is too much “groupthink” in developing tools for climate engineering. You even talk about getting the public involved—how do you envision public engagement taking shape?

DK: An easy but valuable first step is simply to have active experts from scientists to policymakers spend time talking with regular citizens to understand their views. A harder task is to develop ways for groups of citizens to come together to debate the issues in a way that can directly inform policy. But this request for a kind of deliberative distributed democracy is necessarily hard to implement because it threatens the powers of today’s elites.

BR: How do you see the next ten years, in both research and policy, playing out? What direction is research going in, currently?

DK: Solar geoengineering is quickly gaining visibility both within elite technical communities and in the general public. I have no idea what will happen next. Some of my more activist colleagues want to see rapid commitment to implementing geoengineering. I played a small early role, starting more than twenty years ago, in bringing this topic into the public policy dialogue. Yet I am now often afraid that it will move too quickly, and we will see too quick a commitment to either an outright ban or hasty implementation without developing an adequate scientific understanding and, far more important, without developing even a roughly shared collective understanding of what these new powers mean for humanity’s relationship with nature.

Climate scientist David Keith's BR book, A Case for Climate Engineering, is now available from MIT Press. The book provides a clear and accessible overview of what the costs and risks might be, and how climate engineering might fit into a larger program for managing climate change. For more on David Keith's work, check out profiles in the Boston Globe Magazine, Science, Slate and The Washington Post.