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A Magazine of Ideas

Engineering the Climate

From the Magazine: Wednesday, January 14, 2009

Can global warming be stopped? Ask a geoengineer.

Q: What is geoengineering?
A: Many scientists and policymakers have become increasingly pessimistic about the prospects in the near future of sharply reducing global greenhouse gas emissions, so scholars have begun to consider whether there might be other ways to counteract global warming, particularly if it proves to be severe. “Geoengineering” is the most common term for efforts to intentionally change the Earth’s environment in ways that would compensate for the effects of elevated greenhouse gas concentrations. “Climate engineering” might be a better term for this concept.

The basic idea is quite simple. The Earth is warmed by two forces: solar radiation, which enters the atmosphere, and the greenhouse gases that trap it there. There are two possible ways to cool the planet, therefore: reduce greenhouse gases or reduce the amount of solar radiation that reaches the Earth’s surface. If we can’t cut greenhouse gas emissions quickly enough, it makes sense to think about the other source of warming, solar radiation. Reflecting just a small fraction of the incoming sunlight— roughly 2 percent—would be enough to offset the warming effects that we are likely to experience in this century.

Q: Could we really do that? How do you know it would work?
A: It might be premature to say that we know it would work—but the evidence we have so far indicates that it would. The National Academy of Sciences, NASA, the Department of Energy, and several leading academic scientists have studied geoengineering and concluded that it could be (as the National Academy put it) “feasible, economical, and capable.”

The science is still in its infancy, and will remain so until there are field experiments to test the theories and models that scientists are working with today. But Mother Nature has conducted some dramatic experiments that provide a relatively crude but clearly effective demonstration of the basic concept. The 1991 eruption of Mt. Pinatubo in the Philippines, for example, cooled the planet for at least a year by roughly half a degree Celsius. The question for scientists and engineers is how we could artificially reproduce that effect.

Q: What kinds of geoengineering projects could be considered?
A: There are a few different ideas, but the simplest and most commonly discussed one among scientists is mimicking the effects of a Mt. Pinatubo-type volcanic eruption by distributing some kind of ultra-fine particles, such as sulfur, in the upper atmosphere. The particles would block enough incoming sunlight to cool the planet and counteract the effects of warming. Such a system could be tested and initially deployed over the Arctic. If results were promising, it could be expanded; if there were undesirable side effects, the particles would quickly fall to earth once the system was discontinued.

Geoengineering would have to be a complement to, rather than a substitute for, a long-term program to transition to a zero-emissions economy.

An intriguing idea has been proposed by two British scientists, John Latham, an atmospheric physicist, and Stephen Salter, an engineer. Rather than look to volcanoes as the cooling force to be emulated, they noted that low-altitude marine stratocumuli clouds also reflect sunlight. The reflective abilities of these clouds, which cover about 25 percent of the world’s oceans, could be enhanced by a fleet of ships that would spray a fine mist of seawater into the air. Latham and Salter calculate that increasing the reflectivity of those clouds by about 10 percent would be enough to counteract the warming effect of elevated greenhouse gas concentrations.

A much more low-tech way of reflecting some sunlight would be to paint the roofs of buildings white. A provocative new study from three scientists in California calculates that painting 1,000 square feet of roof white would reflect enough sunlight to counteract the warming effects of 10 tons of carbon dioxide. Light-colored pavement can also reflect sunlight. If implemented widely throughout the tropical and temperate regions of the world, this study calculates that enough sunlight could be reflected to offset 44 gigatons of CO2—the equivalent of a year and a half of all global emissions.

Q: Are there ways to engineer the climate that don’t seek to reduce solar radiation?
A: “Ocean iron fertilization” is a way of changing the Earth’s environment to enhance the ability of the oceans to capture and sequester carbon dioxide. The growth of plankton in some parts of the ocean is limited by a shortage of iron. Oceanographer John Martin studied this phenomenon in the 1980s and later famously remarked, “Give me a half a tanker of iron and I will give you another ice age.” That statement is something of an exaggeration, but it does seem clear that significant amounts of CO2 could be sequestered through this technique.

As with other geoengineering techniques, there is a great deal we still don’t know about how effective—and how risky—this might be if it were pursued on a grand scale, but there is intense interest in this idea and I think we will learn a lot from field experiments that are expected in early 2009.

Q: Is the goal to stabilize the Earth’s temperature?
A: The goal would be to reduce the harmful effects of warming as much as possible; whether that means climate “stabilization” per se is another matter, but certainly the extent of warming could be significantly curtailed. Deciding on what average global temperature would be optimal is a complex question that will require careful analysis. By the time policymakers really consider those questions, I hope scientists will know much more about the risks, rewards, and limitations of different geoengineering technologies that might be used and the severity of the harms that we might want to ameliorate. Knowing more about the nature of the problem and the tools we might be able to use to address it should help define the precise goals of a geoengineering program.

Q: Is this a completely new idea? Has geoengineering been tried before, even on a small scale?
A: It is not a new idea. In fact, when President Johnson was first briefed on the possibility of global warming in 1965, the only policy response that was considered at the time was geoengineering. Geoengineering wasn’t taken particularly seriously until recently, but the convergence of two trends has renewed interest: There is growing concern about the potentially serious effects of warming, and growing skepticism about the prospects for large reductions in global emissions in the near future. Given those facts, it would be foolish not to explore the alternatives. As far as we know, no country has attempted geoengineering yet, even on an experimental basis, but I believe it is only a matter of time—and perhaps not much time—before someone does.

Q: Is this a substitute for trying to reduce greenhouse gas emissions?
A: No, although critics of the idea claim that it could be used as an excuse to continue unchecked emissions forever. As a result, there has been a lot of reluctance among scientists to even discuss geoengineering publicly. That concern is badly misplaced. If anything, I believe the deployment of a geoengineering system would only enhance interest in emissions reductions. Geoengineering is an idea with tremendous potential, but it is neither a permanent nor a perfect solution to warming. There are risks to and, more important, limitations on what it can do; it does nothing to alleviate ocean acidification, for instance. So geoengineering would have to be a complement to, rather than a substitute for, a long-term program to transition to a zero-emissions economy.

The 1991 eruption of Mt. Pinatubo in the Philippines cooled the planet for at least a year by roughly half a degree Celsius.

But that does not diminish the value of geoengineering; to the contrary, geoengineering may be the key that makes emissions reductions feasible. Geoengineering could buy us time to make the transition to a zero emissions economy while protecting us from the worst potential effects of warming. It may be possible to find ways to phase out fossil fuels or capture their greenhouse gases—but it will take a very long time. Tom Wigley of the National Center for Atmospheric Research, one of the leading scholars in the field, believes that geoengineering, coupled with a long-term effort to reduce emissions, could stabilize the climate, while doing so through emissions reductions alone would be “virtually impossible.”

Q: If we are worried about the impact of carbon emissions, why not just massively restrict emissions of carbon?
A: If only it were so easy! Every facet of the factual and historical record suggests that it is not, unfortunately. After 20 years of trying to craft national and international programs to reduce greenhouse gas emissions, we have little to show for our efforts other than failure. The Kyoto Protocol would only have slowed global emissions by a barely perceptible rate even if its targets were met; many European countries are far from meeting them. China, India, and other developing economies were excluded from Kyoto and have steadfastly refused to accept any limits on their future emissions, and their emissions are growing at a staggering rate; by 2030, China’s emissions are expected to equal the total global emissions today. Even in wealthy countries such as the United States, few causes are more celebrated today than global warming—and yet, confronted by record-high energy prices already, voters and their representatives are not enthusiastic about boosting those bills any higher.

Q: What are some important things we need to learn soon to find out if this can work?
A: Generally speaking, there are three basic questions about geoengineering that researchers are trying to answer: Would it work? What would be the optimal technology, or mix of technologies? What is the risk of negative side effects, and what might we do to address them?

A fourth interesting question is when we should start to deploy a system. Do we wait until the effects of warming are severe, at which point the degree of correction that would be needed would be greater, or should we be thinking about potential deployment much sooner, on a much smaller scale? It may be tempting to wait longer, since the need for geoengineering would be widely accepted, but it might be better to act sooner.

The key is to start doing some experiments. Scientists are doing good work with models, but field experiments would be invaluable and the risks are low: Since particles in the atmosphere above the Arctic fall to earth quickly, a system could be turned on and off quickly. It would have the additional benefit of reducing Arctic warming, and it would give us vital data to analyze. We could begin with a low altitude experiment over the Arctic and, if the data are reassuring, begin testing a global system.

At the same time, field experiments with other geoengineering techniques such as ocean iron fertilization and the Latham-Salter approach could tell us whether those ideas are worth pursuing as well.

Q: Should we be worried about unintended consequences of geoengineering efforts?
A: Yes, if for no other reason than geoengineering, if pursued on a large scale, would be the most extensive deliberate interference with the global climate—a vastly complex system that we only crudely understand—in human history. That is a daunting proposition. On the other hand, we are already changing the global climate in a similarly unprecedented manner; the only difference is that our current actions are unintentional and uncontrolled.

There are some specific concerns that scientists are exploring. It’s possible that geoengineering might cause disruptions to regional climates such as the Asian monsoon. The potential for droughts is another concern. There is also apprehension that a system that used sulfur particles to block the sun would cause stratospheric ozone depletion. The ozone hole is closing slowly now; a sulfur-based geoengineering system would slow the rate of repair somewhat. Based on what we know so far, none of these concerns seems significant enough to outweigh the potential benefits of geoengineering, should warming prove significant, but much more research is obviously needed.

It is the very fact that this is a legitimate concern, however, that argues most strongly in favor of beginning serious research into these questions now. Given that it seems quite likely that some nation—not necessarily the United States—will want to embark on a geoengineering program in the future, it would be only prudent for us to begin a serious research program soon so we might have as much information as possible to inform those decisions when the time comes.

Q: What kind of investment has been made so far to look into this? What more is needed?
A: As far as we know, there is no government-funded program to research and develop these ideas, either in the United States or abroad. The Department of Energy considered initiating such a program in 2001 but never pursued the idea beyond the staff level. So current research efforts are limited to a few academics using scarce resources. In June, the National Academies of Science of the G-8+5 nations expressed an interest in the field, and that may ultimately help spur greater government attention; but we are probably still several years away from a federally funded research program. If we spent as little as $100 million over five years, conducting some basic experiments, we could learn a great deal about which geoengineering techniques might be most effective, what potential side effects should concern us, and what we might do to reduce those risks. Given that the federal government currently spends about $3 billion a year on researching emissions reduction technologies, the cost of a program to answer our basic questions about geoengineering would be very modest.

Q: What other countries are studying this seriously?
A: That’s a good question. As far as we know, none—but some of the countries that might be most interested are not likely to be particularly open about their research plans. Russia, China, and India are the countries I would expect to be most interested in the field. Many critics of geoengineering are excessively focused on the question of whether America should pursue it, forgetting that countries that are much more vulnerable to warming are quite likely to pursue it themselves. If that proves to be the case, then it would be in our interest to have an extensive base of knowledge to draw upon when decisions about deployment need to be made. With those concerns in mind, my colleague Lee Lane and I are directing a project at the American Enterprise Institute to explore the state of the science and the policy implications of geoengineering. Our goal is to promote greater national and international consideration of the many complex questions that this revolutionary idea raises.

Samuel Thernstrom is a resident fellow at the American Enterprise Institute and co-director of the AEI Geoengineering Project.

Photograph by Dave Harlow.