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October 22, 2012

Scientists Use Geoengineering to Reflect Solar Warming Back into Space



In the era before sunscreen became de rigueur, many beachgoers used aluminum reflectors to “catch some rays” and direct them at their oiled-up bodies to achieve a deeper tan. Now, scientists have considered the benefits of doing exactly the opposite – directing sunlight back at the atmosphere from which it originates – to alleviate the effects of global warming.

Indeed, based on the results of a new study executed by researchers at Harvard School of Engineering and Applied Sciences in Cambridge, Massachusetts; Carnegie Institution for Science in Washington, DC; and California Institute of Technology in Pasadena, California, it may be possible to mitigate the effects of climate change caused by greenhouse gases by using “solar geoengineering,” tailored to reduce heat inequality – or to manage specific risks such as the loss of Arctic sea ice.

By increasing the concentrations of aerosols in the stratosphere or by creating low-altitude marine clouds, the as-yet hypothetical solar geoengineering projects would scatter incoming solar heat away from the Earth’s surface.

If such solar geoengineering were tailored by region and by need, the model promises to maximize the effectiveness of solar radiation management while largely avoiding its potential side effects and risks – according to authors of the study, whose findings appear in the November edition of Nature Climate Change.

Critics of geoengineering have long warned that such a global intervention would have unequal effects around the world and could result in unforeseen consequences. They argue that the potential gains may not be worth the risk.

However, “Our research goes a step beyond the one-size-fits-all approach to explore how careful tailoring of solar geoengineering can reduce possible inequalities and risks,” said coauthor David Keith, Gordon McKay professor of Applied Physics at the Harvard School of Engineering and Applied Sciences (SEAS) and professor of Public Policy at Harvard Kennedy School. “Instead, we can be thoughtful about various tradeoffs to achieve more selective results, such as the trade-off between minimizing global climate changes and minimizing residual changes at the worst-off location.”

The study – developed in collaboration with Douglas G. MacMartin of the California Institute, Ken Caldeira of the Carnegie Institution, and Ben Kravitz, formerly of Carnegie and now at the Department of Energy – explores the feasibility of using solar geoengineering to counter the loss of Arctic sea ice.

Keith noted, “There has been a lot of loose talk about region-specific climate modification. By contrast, our research uses a more systematic approach to understand how geoengineering might be used to limit a specific impact. We found that tailored solar geoengineering might limit Arctic sea ice loss with several times less total solar shading than would be needed in a uniform case.”


Sunset in the Arctic. A new study at Harvard explores the feasibility of using cautious and targeted solar geoengineering to counter the loss of Arctic sea ice. Image via NASA/Kathryn Hansen and Harvard University.

Generally speaking, greenhouse gases tend to suppress precipitation, and an offsetting reduction in the amount of sunlight absorbed by Earth would not restore this precipitation. Both greenhouse gases and aerosols affect the distribution of heat and rain on this planet, but they change the temperature and precipitation in different ways in different places. The researchers suggest that varying the amount of sunlight deflected away from the Earth both regionally and seasonally could combat some of this problem.

“These results indicate that varying geoengineering efforts by region and over different periods of time could potentially improve the effectiveness of solar geoengineering and reduce climate impacts in at-risk areas,” explained coauthor Ken Caldeira, senior scientist in the Department of Global Ecology at the Carnegie Institution for Science.

The researchers noted that while their study used a state-of-the-art model, any real-world estimates of the possible impact of solar radiation management would need to take into account various uncertainties.

Further, any interference in Earth’s climate system, intentional or unintentional, is likely to produce unanticipated outcomes.

“While more work needs to be done, we have a strong model that indicates that solar geoengineering might be used in a far more nuanced manner than the uniform one-size-fits-all implementation that is often assumed,” the authors agreed. “One might say that one need not think of it as a single global thermostat. This gives us hope that if we ever do need to implement engineered solutions to combat global warming, that we would do so with a bit more confidence and a great ability to test it and control it.”




Edited by Braden Becker


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