Stratospheric Aerosols for Solar Radiation Management



SRM in the context of this entry involves placing a large amount of aerosols in the stratosphere to reduce the amount of solar radiation reaching the surface, thereby cooling the surface and counteracting some of the warming from anthropogenic greenhouse gases. The way this is accomplished depends on the specific aerosol used, but the basic mechanism involves backscattering and absorbing certain amounts of solar radiation aloft. Since warming from greenhouse gases is due to longwave (thermal) emission, compensating for this warming by reduction of shortwave (solar) energy is inherently imperfect, meaning SRM will have climate effects that are different from the effects of climate change. This will likely manifest in the form of regional inequalities, in that, similarly to climate change, some regions will benefit from SRM, while some will be adversely affected, viewed both in the context of present climate and a climate with high CO2 concentrations. These effects are highly dependent upon the means of SRM, including the type of aerosol to be used, the particle size and other microphysical concerns, and the methods by which the aerosol is placed in the stratosphere. SRM has never been performed, nor has deployment been tested, so the research up to this point has serious gaps. The amount of aerosols required is large enough that SRM would require a major engineering endeavor, although SRM is potentially cheap enough that it could be conducted unilaterally. Methods of governance must be in place before deployment is attempted, should deployment even be desired. Research in public policy, ethics, and economics, as well as many other disciplines, will be essential to the decision-making process. SRM is only a palliative treatment for climate change, and it is best viewed as part of a portfolio of responses, including mitigation, adaptation, and possibly CDR. At most, SRM is insurance against dangerous consequences that are directly due to increased surface air temperatures.


Arctic oscillation

A pattern of sea-level pressures in the Arctic indicating large-scale circulation patterns. This serves as a proxy for the degree to which Arctic air penetrates to lower latitudes. During a positive mode of the Arctic Oscillation, which occurs both naturally and can be forced by large injections of stratospheric aerosols that enhance the polar jets, cold air gets trapped in the Arctic, resulting in warmer winter temperatures over the northern hemisphere continents.

Carbon dioxide removal (CDR)

Removing carbon dioxide from the atmosphere and sequestering it, either in geological formations or in the deep ocean, thereby decreasing the atmospheric concentration of anthropogenic greenhouse gases.


A convective cloud that forms from a large amount of heating, and subsequent rising air, created by large fires.

Solar radiation management (SRM)

Reducing the amount of sunlight incident at the surface, thereby decreasing the globally averaged surface air temperature of the planet.

Stratospheric aerosols

A layer of aerosols into the stratosphere which either scatter or absorb (or a combination of the two) a certain portion of sunlight that would, under normal circumstances, reach the surface.

Tipping point

The point at which global climate transitions from one stable state to another. Some extreme examples include ice ages, in which the climate rapidly cools, forming large ice sheets. The climate in this state is relatively stable, mainly due to an increase in planetary albedo, and is not easily returned to a different state (the present day climate, for example) without a large forcing of some kind.


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© Springer Science+Business Media New York 2013

Authors and Affiliations

  1. 1.Department of Global EcologyCarnegie Institution for ScienceStanfordUSA

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