How do aerosols affect Earth’s temperature?

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Grinnell Glacier shrinkage — Global warming A series of photographs of the Grinnell Glacier taken from the summit of Mount Gould in Glacier National Park, Montana, in (from left) 1938, 1981, 1998, and 2006. In 1938 the Grinnell Glacier filled the entire area at the bottom of the image. By 2006 it had largely disappeared from this view.

Aerosols generally exert a cooling influence on Earth’s surface by creating a negative radiative forcing. Most aerosols, such as sulfate and nitrate, reflect incoming solar radiation back into space, which reduces the amount of sunlight reaching the surface.1

Aerosols also influence the climate indirectly by modifying cloud properties, often serving as condensation nuclei that facilitate cloud formation. Collectively, these direct and indirect effects provide a significant offset—roughly 40 percent—to the warming caused by greenhouse gases.1

However, not all aerosols cause cooling. Carbonaceous aerosols, such as carbon black or soot, absorb solar radiation and have a warming impact on the lower atmosphere. Furthermore, when carbon black settles on snow, it decreases the albedo of the surface, causing more heat to be absorbed rather than reflected. Because aerosols have short atmospheric residence times compared to greenhouse gases, their cooling effect depends on continuous emissions.1