GEOENGINEERING
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Geoengineering refers to a set of emerging technologies that could manipulate the environment and partially offset some of the impacts of climate change. Solar geoengineering in particular could not be a replacement for reducing emissions (mitigation) or coping with a changing climate (adaptation); yet, it could supplement these efforts.
GEOENGINEERING IS CONVENTIONALLY SPLIT INTO TWO BROAD CATEGORIES:
THE FIRST IS CARBON GEOENGINEERING, OFTEN ALSO CALLED CARBON DIOXIDE REMOVAL (CDR). THE OTHER IS SOLAR GEOENGINEERING, OFTEN ALSO CALLED SOLAR RADIATION MANAGEMENT (SRM) OR ALBEDO MODIFICATION. THERE ARE LARGE DIFFERENCES.
Carbon geoengineering seeks to remove carbon dioxide from the atmosphere, which would address the root cause of climate change — the accumulation of carbon dioxide in the atmosphere. In the chain from emissions to concentrations to temperatures to impacts, it breaks the link from emissions to concentrations.
Solar geoengineering seeks to reflect a small fraction of sunlight back into space or increase the amount of solar radiation that escapes back into space to cool the planet. In contrast to carbon geoengineering, solar geoengineering does not address the root cause of climate change. It instead aims to break the link from concentrations to temperatures, thereby reducing some climate damages.
SOLAR GEOENGINEERING
There are several proposed solar geoengineering technologies. These include marine cloud brightening, cirrus cloud thinning, space-based techniques, and stratospheric aerosol scattering, amongst others. Marine cloud brightening would attempt to brighten marine clouds to reflect more sunlight back into space. Cirrus cloud thinning would attempt to reduce the thin, high-altitude cirrus clouds to emit more long-wave radiation from the earth to space. Space-based technologies would attempt to reflect a small fraction of sunlight away from the earth by positioning sun shields in space. And stratospheric aerosol scattering would introduce tiny reflective particles, such as sulfate aerosols or perhaps calcium carbonate, into the upper atmosphere, where they could scatter a small fraction of sunlight back into space.
SOLAR GEOENGINEERING BENEFITS AND RISKS
Climate models have consistently shown that solar geoengineering, when used in moderation and combined with emissions cuts, has the potential to reduce climate changes around the globe. For example, it could reduce climate impacts such as extreme temperatures, changes in water availability, and intensity of tropical storms.
However, any benefits come with novel risks and significant uncertainty. For example, while the latest science might show some benefits globally, local impacts could vary more widely. There are a lot of other scientific uncertainties that are not yet well understood, not least the enormous governance challenges.
Another problem that solar geoengineering (largely) does not address is ocean acidification. Every year, the ocean absorbs about one-quarter of the carbon dioxide we emit into the atmosphere, changing the chemistry of the oceans and harming marine ecosystems. Given that solar geoengineering would not remove carbon dioxide from the atmosphere directly, but rather reflect sunlight back to space, it could do little to address this serious problem except via carbon cycle feedbacks, the process through which additional carbon is emitted into the atmosphere upon additional warming.
Solar geoengineering, thus, could not be a substitute for cutting carbon dioxide pollution. It could only be a potential supplement.
PUBLICATIONS
Harvard's Solar Geoengineering Research Program seeks to advance natural and social science research on solar geoengineering. The following academic and non-technical publications highlight some of the latest findings.
ACADEMIC PUBLICATIONS
Mahajan, Aseem, Dustin Tingley, and Gernot Wagner. “Fast, cheap, and imperfect? U.S. public opinion about solar geoengineering.” Environmental Politics (2018). Publisher's VersionAbstract
MacMartin, Douglas G., Katharine L. Ricke, and David W. Keith. “Solar geoengineering as part of an overall strategy for meeting the 1.5°C Paris target.” Philosophical Transactions of the Royal Society 376, no. 2119 (2018).Abstract
Dai, Zhen, Debra Weisenstein, and David Keith. “Tailoring Meridional and Seasonal Radiative Forcing by Sulfate Aerosol Solar Geoengineering.” Geophysical Research Letters 45 (2018).Abstract
Keith, David W., Gernot Wagner, and Claire L. Zabel. “Solar geoengineering reduces atmospheric carbon burden.” Nature Climate Change 7 (2017): 617–619. Publisher's VersionAbstractMORE
NON-TECHNICAL PUBLICATIONS
Wagner, Gernot, and Martin Weitzman. “A Big-Sky Plan to Cool the Planet.” The Wall Street Journal, 2018. Publisher's Version
Keith, David W., and Gernot Wagner. “Fear of solar geoengineering is healthy – but don't distort our research.” The Guardian, 2017.Publisher's Version
Keith, David. “Toward a Responsible Solar Geoengineering Research Program.” Issues in Science and Technology 33, no. 3 (2017).Publisher's Version
Burns, Elizabeth, David Keith, Edward Parson, and Gernot Wagner, ed.Report on the Forum on U.S. Solar Geoengineering Research. Washington, D.C. 2017.
