|Enhanced aerosol concentrations can make the clouds more opaque and emit more thermal energy to the surface.|
Two scientists from Scripps Institute of Oceanography and Brookhaven National Laboratory have measured the impact of a significant anthropogenic source of warming: aerosol concentrations in Arctic clouds. The research is published in the current issue of Nature.
The team used radiometric data to show that increased concentrations of aerosols in the clouds cause the cloud droplets to become smaller and, within clouds of fixed water amounts, more abundant. This process, known as the “first indirect” effect makes many clouds more opaque and to emit more thermal energy to the surface by an average of 3.4 watts per square meter, which is comparable to the effect of increased greenhouse gases.
The Arctic is showing the first unmistakable signs of climate warming caused by human activities, in the form of rapidly retreating and thinning sea ice. This rapid climate change in the Arctic may have profound implications for both fragile ecosystems and unique modes of human habitation. Our study illustrates how human activity can influence Arctic climate in more than one way, by changing the way clouds warm the climate, in addition to the carbon dioxide increases. It is also another example of human industrial activity’s surprising impact on remote polar regions, the most famous example being the Antarctic ozone hole discovered in the mid-1980s.—Ray Lubin, Scripps
The Arctic region also experiences significant periodic influxes of anthropogenic aerosols, which originate from the industrial regions in lower latitudes.
Because sunlight is generally weak in the Arctic, the clouds, via their emission of thermal energy, normally exert a net warming on the Arctic climate system throughout most of the year, except briefly during the summer.
“A climatologically significant aerosol longwave indirect effect in the Arctic”; Dan Lubin and Andrew M. Vogelmann; Nature 439, 453–456 (26 January 2006); doi:10.1038/nature04449