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Researchers quantify stratosphere damage with an eye toward ozone hole recovery |
| Theallineed/NC&T/RU |
That's the premise of a paper published in last week's Science titled, "Anthropogenic and Natural Influences in the Evolution of Lower Stratospheric Cooling."
Researchers used a new global ocean-atmosphere model to study the stratosphere, the layer above the troposphere from about 12 to 50 km, and better understand what has contributed to its cooling over the past approximately 25 years. The stratosphere contains the ozone layer, which absorbs sunlight and heats the stratosphere. This long-term cooling trend in the lower stratosphere is generally accepted to result from the loss of the ozone layer as a result of man-made influences. However, the cooling trend is not uniform like ozone loss, but rather broken into a series of jumps or discontinuities. These jumps are associated with major volcanic (El Chichon in 1982 and Mt. Pinatubo in 1991) eruptions that inject aerosols into the stratosphere. The aerosols also absorb sunlight and heat the stratosphere, thus temporarily offsetting the cooling trend from ozone loss. The volcanic eruptions are considered to be a "natural" forcing.
The model that researchers used to evaluate the influences, both man-made and naturally occurring, included not only the ozone loss and volcanic eruptions, but solar activity, greenhouse effect of CO2, and a few other variables that also affect stratospheric temperature. They found that when all these factors are included, the model does an excellent job of reproducing the observed cooling of the stratosphere over the record of satellite observation from 1980 to 2005 - both the long-term cooling trend and the jumps.
"There is growing evidence that current trends in stratospheric circulation and temperature play an important role in global climate change," said Georgiy L. Stenchikov of Rutgers' Cook College Department of Environmental Sciences, who is among the paper's six authors. "The ability of up-to-date models to correctly reproduce the complex processes led to dramatic changes observed in the stratosphere during recent decades fills in the models credibility and helps to better predict future climate variations."
Venkatchalam Ramaswamy, from NOAA's Geophysical Fluid Dynamics Laboratory (GFDL) in Princeton NJ, is the lead author on this paper, which includes the work of Stenchikov, Brian Soden from the University of Miami Rosenstiel School, Dan Schwarzkopf from NOAA's GFDL, Bill Randel from the National Center for Atmospheric Research and Ben Santer from the Program for Climate Model Diagnosis and Intercomparison at Lawrence Livermore National Laboratory, and Georgiy Stenchikov at the Department of Environmental Sciences at Rutgers University.
Increasing carbon dioxide warms the earth's surface and troposphere, but cools the stratosphere. In the next century, carbon dioxide will likely become the dominant contributor to stratospheric cooling. The change in the stratospheric temperature distribution also affects stratospheric circulation that could amplify direct radiative effects. Future stratospheric cooling, especially in polar regions, may have important implications for the rate of recovery of the ozone hole in the southern hemisphere and possibly even the loss of ozone over the polar regions of the northern hemisphere.
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