Global Science Report is a feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”
Currently, details are few, but apparently the results of a major scientific study on the effects of anthropogenic aerosols on clouds are going to have large implications for climate change projections—substantially lowering future temperature rise expectations.
In a blog post from the Department of Meteorology of the University of Reading, Dr. Nicolas Bellouin describes some preliminary results from a research study he leads that is investigating the influence of aerosols on cloud properties. The behavior of clouds, including how they are formed, how long they last, how bright they are, etc., plays a very large role in the earth’s climate system, and is considered the weakest part of global climate models. The climate model cloud deficiency results from a combination of scientific uncertainty about cloud behavior, as well as the modeling challenges that come from simulating the small spatial and temporal scales over which the important processes take place.
When it comes to the influence of human aerosol emissions on cloud properties, the scientific mainstream view is that aerosols modify clouds in such a way as to result in an enhanced cooling of the earth’s surface—a cooling influence which has acted to offset some portion of the warming influence resulting from human emissions of greenhouse gases (primarily from the burning of fossil fuels, like coal, oil, and natural gas to produce energy). In the absence of this presumed aerosol cooling effect, climate models predict that the earth should warm at a much faster rate than has been observed. A large cooling effect from aerosols was thus introduced in the early 1990s as a way to “fix” the climate models and bring them closer in line with the modest pace of observed warming. Despite that “fix,” climate models continue to overpredict the observed warming rate—which is bad enough news for climate models already.