Harvard professor David Keith has done as much as any single researcher to push the touchy topic of geoengineering toward the scientific mainstream (see “A Cheap and Easy Plan to Stop Global Warming”).

He was among the first to seriously assess potential ways of altering the climate to ease global warming, and he has undertaken some of the most detailed research on a promising approach known as stratospheric injection. He also wrote a book on the subject, A Case for Climate Engineering, and co-manages a Bill Gates–backed energy and climate fund that has supported research in this area. This year, Keith helped launch Harvard’s Solar Geoengineering Research Program, and announced plans with a colleague to carry out what would be among the earliest outdoor experiments in the field (see “The Growing Case for Geoengineering”).

The basic idea behind stratospheric injection is that spraying particles high above the Earth could help reflect more heat back into space, offsetting rising temperatures. It would mimic a natural phenomenon that occurs when large volcanic eruptions blast sulfur dioxide into the atmosphere, which nudges down global temperatures in the months that follow.

For the proposed experiment, Keith and fellow Harvard professor Frank Keutsch plan to launch high-altitude balloons that would spray small amounts of materials such as sulfur dioxide, alumina, or calcium carbonate into the stratosphere. They would then employ sensors to measure the reflectivity of the particles, the degree to which they disperse, and how they interact with other compounds. Initial test flights could occur as early as next year.

Listen to a conversation with David Keith on using geoengineering to address the threat of climate change.

Keith, a professor of applied physics and public policy at the university, sat down with MIT Technology Review earlier this year to discuss the upcoming experiments, and broader issues surrounding geoengineering. We’ve included highlights from that interview in the audio player below; the text follows.

Keith will also be a speaker at the publication’s EmTech 2017 conference, November 6–9 at the MIT Media Lab in Cambridge, Massachusetts, where we’ll continue the conversation on geoengineering and other means of addressing the growing risks of climate change.

Why is it time to move forward with geoengineering field trials?

I think it’s time to move forward with a broad research program on solar geoengineering, one that is open-access and international and transparent. And that’s because there is a real chance—we don’t know—that it might be able to substantially reduce climate risk this century. But it raises hard governance challenges, and we don’t know the risks or how well it works. We need to know that so we can give the information to the next generation so they can make good decisions. That’s the fundamental reason to have a research program.

The answer to why do outdoor experiments is because that’s a normal part of research. In any kind of environmental research, you have to do a mixture of building careful theoretical models and then going out and making careful controlled experiments to understand where those models go wrong. The big issue here is really to understand how we’re wrong, and you do that ultimately by setting up carefully controlled experiments that are quantitative, where you can see errors in your prediction.

And from my point of view, it’s wrong to think about this as a trial of geoengineering. What a field trial would mean to me is that you had the full system you wanted to deploy, and you were beginning to deploy it in some trial mode to see if it worked. That is absolutely not what we’re doing. At this point, it’s much too early to think about engineering a complete system for deployment. I would oppose that. We’re trying to do science to help us understand how well some solar geoengineering ideas might work, how they might fail, what their risks might be.

Even geoengineering critics—or at least credible geoengineering critics, I guess—seem to agree that [at this small scale], the trials being discussed don’t pose any significant environmental risk. But one of the main criticisms that remains, and the one that you hear about a lot, is the idea of “moral hazard” — or I think the term you prefer is “risk compensation.” This basic idea that people and policy makers will see these serious, well-credentialed scientists doing this work and say, “Oh, well, they’ve got this,” and therefore we don’t need to take greenhouse gas reductions as seriously. What's your response to that argument?

First of all, it’s important to say that that argument doesn't apply to experiments any more than it does to speech. I think at some level it’s a realistic risk that if the scientific community overstates the case that solar geoengineering really could work, there is a chance that it will be used politically to weaken efforts to cut emissions. I think that’s a sensible thing to worry about. But I don’t think there’s any bright line between a small science experiment and, say, a movie or a big public talk or, for that matter, the former chief advisor to the [UN] secretary general starting a major effort on governance. All those things make this look more serious, and I don’t think these concerns apply in a special way to experiments, which in some sense don’t physically do anything different than existing scientific experiments.

In thinking about the moral-hazard argument, you have to weigh two things. Yes, there is some legitimate possibility that it would reduce commitments to cut emissions, but there’s also some possibility that it could substantially reduce climate risk over this century. And in the end, we don’t make that decision on either thing. This is about giving more information to the next generation that will make the serious decisions about this—not us.

You made an interesting point in your book on this issue. You basically said that the moral-hazard argument is probably correct, as you were just saying, but that we should pursue research anyway because the risks of climate [change] are so high. And specifically those risks, which can be kind of treated as sort of an abstraction in the moral-hazard argument, basically boil down to a lot of death and destruction in poor countries. Can you explain that point?

Sure. One of the reasons I’m particularly interested in developing the possibility of solar geoengineering is that it does appear that the benefits are most felt by the poorest. And that’s because the biggest climate impacts—particularly impacts from extreme heat and extreme precipitation events like tropical cyclones—fall on the world’s poorest. And there is now pretty clear evidence that solar geoengineering would be remarkably effective in reducing some of those risks, and the relative benefits [would] actually go more to the poor than to the rich. For me it’s a fundamental ethical reason that we do need to develop the technology to do it, and that we need to engage deeply with people in the developing world, in getting their input into what this development looks like and in diffusing the technology. This may be being developed here, but it’s open-access, and I don’t actually think it’s likely that the U.S. will be the country that deploys. It’s much more likely to be poor countries.