NPR: Could Cleaner Air Actually Intensify Global Warming?

Could Cleaner Air Actually Intensify Global Warming?

by NPR Staff

April 25, 2010

As much of the world marked Earth Day this past week, the Environmental Protection Agency reported that air pollution has declined dramatically over the last 20 years. It sounds like good news, but science writer Eli Kintisch argues that there's a surprising downside: Cleaner air might actually intensify global warming.

"If we continue to cut back on smoke pouring forth from industrial smokestacks, the increase in global warming could be profound," Kintisch writes in an opinion piece for the http://www.latimes.com/news/opinion/commentary/la-oe-kintisch18-2010apr18,0,3774828.story">Los Angeles Times.

Kintisch isn't talking about greenhouse gases like carbon dioxide; he's talking about another kind of pollutant we put in the sky -- "like aerosols from a spray can," he tells NPR's Guy Raz. "It turns out that those particles have a profound effect on maintaining the planet's temperature."

Greenhouse gases and aerosol pollutants work in opposing ways on the Earth's climate, Kintisch explains. "The greenhouse gases warm the planet when they're emitted, because they absorb heat reflected up from the ground -– the greenhouse effect. These aerosols, though, do the opposite. They block sunlight, they make clouds more reflective -- and by doing that, they actually cool the planet.

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Yet, the Academy's report tells us that we do not know how much effect natural fluctuations in climate may have had on warming. We do not know how much our climate could, or will change in the future. We do not know how fast change will occur, or even how some of our actions could impact it.

For example, our useful efforts to reduce sulfur emissions may have actually increased warming, because sulfate particles reflect sunlight, bouncing it back into space. ...

Science 9 July 1971:
Vol. 173. no. 3992, pp. 138 - 141
DOI: 10.1126/science.173.3992.138

Atmospheric Carbon Dioxide and Aerosols: Effects of Large Increases on Global Climate

S. I. Rasool ¹ and S. H. Schneider <sup>1

1</sup> Institute for Space Studies, Goddard Space Flight Center, National Aeronautics and Space Administration, New York 10025

Effects on the global temperature of large increases in carbon dioxide and aerosol densities in the atmosphere of Earth have been computed. It is found that, although the addition of carbon dioxide in the atmosphere does increase the surface temperature, the rate of temperature increase diminishes with increasing carbon dioxide in the atmosphere. For aerosols, however, the net effect of increase in density is to reduce the surface temperature of Earth. Because of the exponential dependence of the backscattering, the rate of temperature decrease is augmented with increasing aerosol content. An increase by only a factor of 4 in global aerosol background concentration may be sufficient to reduce the surface temperature by as much as 3.5 ° K. If sustained over a period of several years, such a temperature decrease over the whole globe is believed to be sufficient to trigger an ice age.