This graph shows estimates of the influences of various factors (greenhouse gases, ozone, aerosols, and other) on climate change over the industrial period, and their combined total influence. Red brackets indicate the range of uncertainty for each factor and the total. The uncertainty for the "total" estimate is so large because of the large uncertainty in the estimated influence of aerosols. Shrinking the uncertainty associated with the total to a value that is useful for interpreting Earths climate sensitivity requires a major reduction in the uncertainty associated with the influence of aerosols.
Climate scientists agree that atmospheric carbon dioxide (CO2) has increased about 35 percent over the industrial period and that it will continue to rise so that CO2 will reach double its pre-industrial value well before the end of this century. How much this doubled CO2 concentration will raise Earth’s global mean temperature, however, remains quite uncertain and is the subject of intense research — and heated debate.
In a paper to be published in the November issue of the Journal of the Air and Waste Management Association, Stephen Schwartz, an atmospheric scientist at the U.S. Department of Energy’s Brookhaven National Laboratory, argues that much of the reason for the present uncertainty in the climatic effect of increased CO2 arises from uncertainty about the influence of atmospheric aerosols, tiny particles in the air. Schwartz, who is also chief scientist of the Department of Energy’s Atmospheric Science Program, points out that aerosols scatter and absorb light and modify the properties of clouds, making them brighter and thus able to reflect more incoming solar radiation before it reaches Earth’s surface.
“Because these aerosol particles, like CO2, are introduced into the atmosphere as a consequence of industrial processes such as fossil fuel combustion,” says Schwartz, “they have been exerting an influence on climate over the same period of time as the increase in CO2, and could thus very well be masking much of the influence of that greenhouse gas.” However, he emphasizes, the influence of aerosols is not nearly so well understood as the influence of greenhouse gases.
Karen McNulty Walsh | EurekAlert!
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