As concerns grow about how quickly the world can curb greenhouse-gas emissions, some scientists want to research an additional approach to the problem of global warming: solar geoengineering.
In contrast to preventing heat-trapping emissions from being added to the atmosphere, solar geoengineering tries to diminish the amount of sunlight reaching the Earth and warming it up. For instance, one hypothetical method would be to regularly add tens of thousands of tons of sulfate particles to the stratosphere, which would bounce more incoming solar radiation back into space and reduce surface temperatures.
Part of the trouble, scientists say, is that solar geoengineering—just one of many types of geoengineering—hasn’t been tested, and it risks disrupting complex climatic processes. To better understand the risks and benefits, a committee of the National Academies of Sciences, Engineering, and Medicine recommended in March that the U.S. invest up to $200 million in a new solar-geoengineering research program, subject to public input and with careful governance over outdoor experiments. But in April, a long-delayed field experiment involving a balloon release over Sweden—designed by Harvard University researchers and funded by private philanthropists—was halted in the face of opposition by environmental and indigenous groups.
These events have lent urgency to several questions: Under what circumstances could solar-geoengineering technology be effectively deployed? Would further research on the risks of geoengineering restrain policy makers from deploying it irresponsibly or set them on a course to doing so? And given that humankind shares one atmosphere, who has a say in whether and how solar-geoengineering research occurs?
In a roundtable discussion conducted via video chat, The Wall Street Journal invited three experts about the issue to weigh in:
a professor of philosophy at Colorado College and part of the National Academies committee;
an atmospheric chemist at Harvard and the principal investigator of the Swedish field experiment; and
a physics professor at the University of Oxford and a prominent critic of geoengineering research.
What follows are edited excerpts of their conversation.
Assessing the risks
WSJ: What are the potential benefits of solar geoengineering, and why are people even considering it?
DR. HOURDEQUIN: It has the potential to offset some of the warming caused by anthropogenic climate change and to tamp down some of the associated effects, such as more frequent heat waves and higher-intensity storms.
DR. KEUTSCH: Solar climate intervention could be viewed as a way of reducing climate risk while humanity is, too slowly, battling the causes of climate change. In addition, the cost is very modest compared with the costs of removing carbon dioxide or changing energy infrastructure.
WSJ: And what about the risks?
DR. PIERREHUMBERT: The biggest physical risk is the risk of termination shock, which is the very rapid catastrophic warming that would occur if solar geoengineering was ever terminated abruptly in a situation where it was being relied on to offset a major portion of the global warming induced by carbon-dioxide emissions. The main sociopolitical risk is that research would undercut nascent efforts to decarbonize the world economy, which is the only real solution to the climate crisis.
DR. HOURDEQUIN: Solar geoengineering could disrupt Asian monsoons, alter agricultural production, slow recovery of the ozone hole or change the productivity of the ocean. There are risks that the concentration of research effort in North America and Europe will generate political polarization around this topic internationally, which may in turn affect broader progress on climate change. There are ethical risks associated with the effects of solar geoengineering on present and future people and ecosystems, as well as risks that decision-making processes may be unfair or not sufficiently inclusive.
WSJ: Should we pursue further research into solar geoengineering?
DR. KEUTSCH: We don’t know enough, so it is critical to find out. Based on models, solar geoengineering has the potential to greatly reduce climate risk. We need studies to learn more about this, get more regional detail, including values that are important for stakeholders and to poke holes in this.
DR. HOURDEQUIN: Almost no one thinks solar geoengineering is an unmitigated good, and many see geoengineering as bad because they don’t think it could ever be governed well or fairly, or because the risks and uncertainties are too great. Even the most sanguine about geoengineering generally see it as a stopgap measure at best.
Research won’t eliminate the risks and uncertainties, but it may help us understand them better. Further study and discussion might make clear that this is simply not a good path to pursue.
DR. PIERREHUMBERT: Because any reliance on solar geoengineering to offset a major portion of global warming would put the world in a precarious state at risk of rapid catastrophic warming in the event of a termination of the deployment, solar geoengineering can only play a very minor role in the portfolio of responses to global warming. Even this minimal potential role would be viable only in a world capable of orderly fact-based global cooperation, and then only after net carbon-dioxide emissions have been brought to zero. Set against its minimal potential role, the risk that expanded solar-geoengineering research might undercut nascent efforts to decarbonize is unacceptable at this time.
WSJ: By researching solar geoengineering, would we set ourselves on a course to using it?
DR. KEUTSCH: I am not convinced that there is a path to limiting global warming to 1.5 degrees Celsius based purely on emission reductions. I am doing this research not because I think we should be doing stratospheric geoengineering, but rather because I am concerned that solar-geoengineering technologies could be deployed even in the absence of research. My personal belief is that the risk of not doing the research is higher than doing that research.
DR. PIERREHUMBERT: Although I’m completely sympathetic to Frank’s idea that someone might just up and do this—because it wouldn’t take that long to develop the technology to just dump some stuff in the stratosphere—I don’t see what kind of research actually addresses that risk.
The National Academy of Sciences recently recommended the study of geoengineering as a possible supplement to reduced CO2 emissions and other climate-change strategies. Here are three methods.
Increase the amount of small particles in the stratosphere to reflect more incoming sunlight.
Modify high-altitude clouds to allow more heat to escape the atmosphere.
Add particles to make low-lying clouds more reflective over certain regions of the oceans.
It’s true that some research is happening already. But if you dump $200 million into this, a lot more research is going to happen. And it also will increase the legitimacy: It’s got a kind of stamp of approval, builds a community that has a stake in doing the research, and maybe even seeing it deployed.
Even if scientists with the best of intentions are clear about how this should or should not be used, you are increasing the risk that somebody will use it. And once the technology is out there, the scientists won’t be the ones making the decision.
WSJ: Your view is that we should take some areas of solar-geoengineering research off the table?
DR. PIERREHUMBERT: We have examples of technologies that large parts of the world have decided simply should not be further developed. The Nuclear Test Ban Treaty: We have actually put something in place that said that this kind of experiment shouldn’t be done. There are problems with compliance, but there is a stated principle. If you want to inhibit the development of something, one way is to just keep it in the laboratory and in the computer.
DR. HOURDEQUIN: The National Academies report does allow for outdoor experiments, but it doesn’t focus on them as the central pillar of any solar-geoengineering research program. In fact, it says outdoor experiments should only be done when they would provide knowledge that cannot be obtained through other means. So, if you can’t get the relevant information through modeling experiments or through smaller-scale lab experiments, then it might be appropriate to pursue outdoor experiments—under a permitting system, and involving social and environmental assessments.
And the budget for solar-geoengineering research should be a very small part of the overall U.S. global climate-change research budget.
DR. PIERREHUMBERT: In my ideal research program, we should be pushing much harder on carbon-dioxide removal. I’d rather see $200 million more go into carbon-dioxide removal than go into starting a big research program on solar geoengineering.
WSJ: What lessons do you take from Sweden’s decision to call off the recent experiment?
Share Your Thoughts
After reading this discussion, are you more or less receptive to considering geoengineering? Join the conversation below.
DR. KEUTSCH: Our actual balloon experiment would have had zero physical impact. What I learned from Sweden is that, for good reasons, this societal engagement and deliberation process is really important. And now it seems quite obvious.
DR. PIERREHUMBERT: How did it happen that you thought of going to Kiruna without even thinking to ask the local people about how they felt?
DR. KEUTSCH: It was a mixture of naiveté and stupidity. I did have a gut feeling about this, and I should have listened, and I didn’t. So, I can tell you it was a mistake.
DR. HOURDEQUIN: It wasn’t at all surprising to me that people objected; people care about much more than physical risks. Thinking about an analogy here, you might ask: Could you do a science experiment in my backyard? You could assure me that it wasn’t going to have any negative, physical impacts on my yard or the aesthetics or anything like that. But I still might want to know what’s it for, and I might feel differently if you’re saying, “It’s just the initial stages of building a nuclear bomb” or “It’s the initial stages of developing a coronavirus vaccine.” People are going to have different responses depending on how a particular piece of research fits into a broader agenda.
Mr. Alcorn is a writer in New York. He can be reached at email@example.com.
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