Science 333, 866–870 (2011)

Credit: © BRYAN BUSOVICKI/SHUTTERSTOCK.COM

Increasing concentrations of light-scattering aerosols in the stratosphere during the past decade may have slowed the pace of global warming, a study suggests.

Using data gathered by a variety of satellites and ground instruments, John Daniel, an atmospheric scientist with the National Oceanic and Atmospheric Administration in Boulder, Colorado, and his colleagues assessed recent trends in stratospheric aerosols. From 2000 to 2010, those aerosols increased, on average, by about 7% each year, decreasing global radiative forcing by about 0.1 W m−2 and, correspondingly, global average temperatures by about 0.07 °C. This cooling effect helped counteract about 20% of the warming that would have occurred without these aerosols, the researchers contend.

It isn't clear what is responsible for the increase in stratospheric aerosols — volcanic eruptions are one possible source — nor is it yet possible to determine the proportion attributable to humans, the researchers report. If during the coming decade the concentration of stratospheric aerosols drops back to levels seen in 1960, global average temperatures would rise by an additional 0.06 °C, they estimate.