Magazine, Vol. 4: Changing Climate
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“Solar Geoengineering is not a solution for climate change”

Glacial, Icecap and Permafrost Melting XXXVI: Bellingshausen Base, King George Island, Antarctica, 2008 © Sayler/Morris

Geoengineering – A Glimpse of Hope, but not the Solution


Solar Geoengineering seeks nothing less than to modify the atmosphere of our planet in order to make it more reflective to sunlight. Rather than mitigating the greenhouse effect itself, it is supposed to decrease the amount of sunlight that enters the greenhouse Earth in the first place. Gernot Wagner, the executive director of Harvard’s Solar Geoengineering Research Program, explains the basic principles, the state of research as well as the opportunities and dangers of this idea. 

Professor Wagner, as the co-director of Harvard’s Solar Geoengineering Research Program, what is it that you’re trying to engineer?

Ideally, we’d all like to engineer sensible climate policy—now. Specifically, though, our research on Solar Geoengineering is about exploring the possibility of building an artificial sunshade for the planet. How would one reflect a tiny portion of sunlight back into space in an attempt to cool the planet?

How does it work?

There are various ways to make the planet more reflective. Why do people wear white in the summer and black in the winter? The reason is that white reflects sunlight and black absorbs it. You cool yourself in the summer by wearing a white t-shirt. That’s the basic principle. Painting roofs white has the same effect on a larger scale, still locally, though.

How would that work for the entire planet?

Ideally, what one would like to achieve is to turn down the sun uniformly, globally. The most prominent method usually discussed revolves around substances called stratospheric aerosols. The idea is to introduce these tiny reflective particles into the lower stratosphere, in order to reflect a small portion of sunlight back into space. The best analogy here are volcanoes. After Mount Pinatubo in the Philippines erupted in 1991, average global temperatures in 1992 were about 0.5 °C cooler because of the resulting sulfate aerosols in the stratosphere. They all fall out again after about eighteen months, so global temperatures in 1993 were again as warm they had been without the volcano. Of course, all of that is just an analogy. Solar engineering is not about exploding artificial volcanoes. It might involve specifically designed airplanes in order to disperse the material in the lower stratosphere.

Consequently, we are talking about a continuous, long-term effort since these substances would have to be renewed on a regular basis? 

Yes, indeed. There’s also another important feature to consider. It turns out the direct engineering costs—how much it costs to lift the material into the stratosphere—is very, very cheap. According to our one rough estimate, we are talking about less than $10 billion per year to do what, for example, Pinatubo has done; to lower global temperatures by around 0.5 °C.

Solar Geoengineering has the exact opposite properties of mitigating CO2 emissions in the first place. Climate change mitigation is akin to a massive coordination effort that is global, long-term, and expensive. It’s the world’s most perfect problem. By comparison, solar geoengineering is often described as “fast, cheap, and imperfect.” That last term is important, too, as it does not address the root cause.

So it’s not supposed to be a solution for climate change?

No, absolutely not. You could think of it in terms of a medical metaphor. We all know that we should diet and exercise. Eat your kale, and run thirty minutes every morning. We also know that most people don’t do either. Now you have this seventy-year-old overweight heart patient, our earth, and the big question is: what to do? Of course, the doctor will advise him to diet and exercise. But at that stage, what will prolong that person’s life for longer is to pop a pill of statins a day to lower his cholesterol level and to decrease the risk of a heart attack. That is akin to solar geoengineering. It is not a replacement for diet and exercise – for cutting emissions. Solar Geoengineering is not a solution for climate change. It may help buy us time and do some good in the process. But that’s about it. It is not a solution.

If we’re unable to install a working, compulsory global arrangement to cut CO2 emissions, why would a global geoengineering scheme work?

Here is one answer, which is less than ideal, but it’s a crucial consideration in this less-than-ideal policy world of ours: It’s not necessary to have a global plan for solar geoengineering to happen. Global coordination would, of course, be the ideal scenario. But we don’t live in an ideal world, where everything happens in a logical, rational manner. That said, back to the aforementioned properties: It’s fast, cheap, and imperfect. The second—“cheap”—is key here. It’s so cheap that there are lots of countries one could imagine pulling the trigger. So it’s certainly possible to imagine a scenario where the technology gets used without these perfect governance systems in place. So while clearly desirable, global arrangement is not a precondition for deployment here.


“Hundreds of thousands of tons of sulfate aerosols in the stratosphere could help offset the average global warming effects”


But would efforts on a local level, affect the entire world?

Yes, they could. Climate is global. Much like emitting a ton of CO2 anywhere affects the climate everywhere, certain forms of solar geoengineering, too, have these global effects. And these effects are much more powerful than with CO2 emissions—orders of a magnitude more powerful. Hundreds of thousands of tons of sulfate aerosols in the stratosphere could help offset the average global warming effects of billions of tons of CO2. The leverage is amazing—not in the positive sense of the word, but in terms of sheer power.

How far has the research on Solar Geoengineering at Harvard University progressed? Have there been any open air experiments?

Not yet, but things are indeed moving in that direction. There’s funding now for a project called SCoPEx (Stratospheric Controlled Perturbation Experiment), led by atmospheric chemist Frank Keutsch. He and colleagues are designing a small-scale experiment involving a balloon flown into the lower stratosphere in an effort to measure impacts in the real world.

What if the experiment goes wrong?

Well, this isn’t about trying to change the temperature. Even if sulfate aerosols were involved, the experiment would release fewer sulfates than one commercial airplane releases in one minute of flight. There are forty thousand of these planes up there today over the US. But, of course, this experiment is indeed a symbol of something much bigger. While the scientific aspect is important, lots of the conversation is really about what this kind of experiment represents. The sensationalist headlines write themselves, and many have already been written. Meanwhile, we do not yet know when—and, frankly, even if—the experiment will, in fact, happen. There are lots of governance questions to consider, including by a formal, external advisory panel.

How long will it take until the technology allows for global Solar Geoengineering that effectively cools the planet?

In some sense, the technology exists already to be doing this in a rather dumb, premature, and woefully misguided way. Volcanoes have been doing this forever. But that’s a rather dangerous thought. There’s lots of research that’s needed—not least on the social science side of things to explore the all-important governance questions. But would it be technically feasible to design the kind of planes that would be able to do this soon? Yes. Would it be desirable? Probably not. Nobody working here as a researcher would propose to use it soon.

Why might it be deployed sooner than one would hope?

Imagine a mid-sized country particularly affected by climate change, perhaps one located in the tropics. Now there’s the umpteenth “hundred-year” storm hitting yet again, perhaps the third within twelve months. The national security advisor to the president might be remiss not to mention the possibility: “We are not a hundred percent sure whether this thing will decrease the storm’s intensity, but we are desperate. So let’s try something, anything.” This may well be the likeliest deployment scenario. And nobody knows whether that is going to happen in ten or fifteen or twenty years, but it would indeed be technically feasible for a country to engage in such a sizeable crash deployment program. Here, we are interested in doing the research because the technology is out there, but the full ramifications are still unknown, especially also of such a hasty deployment scenario. And, of course, ideally, solar geoengineering would be used much more rationally and sensibly. So we better do the research in order to figure out how to actually do it responsibly, or whether it is desirable to contemplate doing it in the first place. And even if not, there’s always that possibility of the rogue actor.

Are you afraid that your research will be hijacked by the fossil fuels lobby in order to change the public perception of climate change? It might argue that we don’t have to stop using fossil fuels if we can artificially cool the planet.

You’ve put your finger on one of the biggest fears out there when it comes to Solar Geoengineering. It often comes under the heading of “moral hazard” and is one of the reasons why there are lots of social scientists interested in the topic: To study this “moral hazard” phenomenon, to study governance, to study all these other questions that are a crucial part of this conversation. Of course, we need to get the technical side right, the engineering, the risk assessment, but that is only one aspect of what is necessary. The social aspect is at least as important and involves more public conversations and research projects than the “narrow” scientific and technological questions.

In the context of moral hazard, the big question we have to ask is: Could the mere conversation about this topic detract from the need to mitigate CO2 emissions in the first place? To some extent, the trade-off between Solar Geoengineering and mitigation is, in fact, rational. If your doctor tells you to exercise for 30 minutes a day and he also tells you that you can pop a cholesterol-lowering pill, it might well be rational to now work out for, say, 29 ½ minutes instead of the 30 recommended without the pill. Of course, the real problem is: Nobody exercises 30 minutes a day. There is a bunch of enthusiasts who exercise 60 minutes a day. Those are the environmentalists. And they are already doing the right thing. They will continue to shout “carbon taxes!” left and right and vote accordingly. The real problem is that the vast majority of us doesn’t exercise at all, that is to say, does way too little when it comes to mitigation. That’s the classic “free rider” problem: None of us has enough of an incentive to do enough.


“Solar Geoengineering could be a wake-up call to increase efforts in terms of mitigation”


But isn’t Solar Geoengineering going to increase our ignorance of climate change by making it seem less threatening?

Perhaps, or it might do the exact opposite. Call it “inverse moral hazard.” There are indeed too many who do not believe that climate change even exists. Again, moral hazard is real. In some sense, the trade-off is ever-present, and yes, there’s the behavioral trade-off: We researchers mention Solar Geoengineering, and the fossil fuel companies say: “Ha, we can keep on pumping. There’ll be a techno-fix!” However, the opposite may also hold true: If you tell people about Solar Geoengineering and they have never heard of this topic before, their reaction may as well be to say “Wait! If such technology is being developed and if serious people are talking about this, maybe there is something to this climate problem after all!” Solar Geoengineering could, thus, be indeed a wake-up call to increase efforts in terms of mitigation. Some good research points to both possibilities. The big question really is which applies under which circumstances, and—normatively speaking—how to get people to want to do more mitigation when they hear about Solar Geoengineering.

The criticism coming from the left is that the entire idea of Solar Geoengineering does not break with the capitalist narrative of endless growth and development. It is an attempt to solve a problem that is the result of technology with more technology. How would you respond to that?

Well, to be clear, we do need to cut CO2 emissions. We have to price CO2. We have to guide market forces in the right direction. And I realize that Solar Geoengineering appears to be an easy way out. It is not. Just because the direct costs alone are low does not mean it’s a good idea. And just because it’s cheap compared to mitigation does not mean we should do it instead of mitigation. At best, it can be a complement to mitigation. Just because chemotherapy is available, doesn’t mean we should keep smoking. And yes, there are certainly those who look at Solar Geoengineering and say “Oh, that’s the easy way out. It gives us a way out that we shouldn’t have, that we shouldn’t want to have.” The most direct answer to that, I’d say, is: Too late. For one, we have known about this possibility for a long time. The very first report on climate change to a US president was for Lyndon B. Johnson, in 1965. This report mentions one solution, and it wasn’t CO2 taxes. It was albedo modification, which in that particular instance referred to the brightening of oceans to reflect more sunlight. By now we pretty much know that that wouldn’t be technically feasible, and there would be lots of other ecological and other consequences that make that idea impractical, to say the least. Nevertheless, geoengineering has been part of this conversation from the very beginning. That said, there had been a 50-year-long taboo around this topic, and in part for good reason, precisely because of this fear that it would detract from the need to mitigate emissions. Solar Geoengineering isn’t a new idea. It’s not something a couple of scientists pulled out of thin air ten years ago, and now the topic is exploding. It has been around for a long time.

Of course, now that there is more research happening, it also draws more attention, especially journalistic attention, which is why we are talking right now. And yes, finding the right framing for this conversation is crucial. Solar Geoengineering is not a solution to climate change, and it must not be presented that way. All that said, we cannot pretend this idea doesn’t exist, and yes, when done sensibly, it may actually do a lot of good, too.

Interview: Jonas Hermann



Rose Lincoln Photo

Gernot Wagner is an economist and the executive director of Harvard’s Solar Geoengineering Research Program. His research is concerned with the economic, social, and political consequences of climate change. Together with Harvard’s Martin L. Weitzman, he has recently published Climate Shock: The Economic Consequences of a Hotter Planet (2016). Wagner is moving to New York University this summer, taking up a post joint between the Department of Environmental Studies and the Wagner School of Public Service.

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