Ozone depletion seen as bigger factor than greenhouse gas forcing
By Summit Voice
SUMMIT COUNTY — After running a complex set of climate models, Penn State researchers concluded that ozone depletion has been the biggest driver in shifting the southern hemisphere jet stream toward the South Pole.
By including short-term wind pattern changes in their calculations, and comparing changes in four different types of wind patterns, the scientist said they were able to determine that the buildup of greenhouse gases in the atmosphere plays a lesser role in the observed changes in the southern hemisphere.
“Previous research suggests that this southward shift in the jet stream has contributed to changes in ocean circulation patterns and precipitation patterns in the Southern Hemisphere, both of which can have important impacts on people’s livelihoods,” said Penn State meteorology professer Sukyoung Lee.
“Understanding the differences between these two forcings is important in predicting what will happen as the ozone hole recovers,” she said. “The jet stream is expected to shift back toward the north as ozone is replenished, yet the greenhouse-gas effect could negate this.”
“When most people look at ozone and greenhouse gases, they focus on one wind pattern, but my previous research suggests that, by looking at several different but similar patterns, you can learn more about what is really happening,” said meteorology professor Steen Feldstein.
In addition to their novel inclusion of more than one wind pattern in their analysis, the scientists investigated the four wind patterns at very short time scales.
“Climate models are usually run for many years; they don’t look at the day-to-day weather,” Feldstein said. “But we learned that the four wind patterns fluctuate over about 10 days, so they change on a time scale that is similar to daily weather. This realization means that by taking into account fluctuations associated with the daily weather, it will be easier to test theories about the mechanism by which ozone and greenhouse gases influence the jet stream.”
“Ozone had the bigger impact on the change in the position of the jet stream,” said Lee. “The opposite is likely true for the Northern Hemisphere; we think that ozone has a limited influence on the Northern Hemisphere. Understanding which of these forcings is most important in certain locations may help policy makers as they begin to plan for the future.”
In addition to finding that ozone is more important than greenhouse gases in influencing the jet-stream shift, the scientists also found evidence for a mechanism by which greenhouse gases influence the jet-stream shift. They learned that greenhouse gases may not directly influence the jet-stream shift, but rather may indirectly influence the shift by changing tropical convection, or the vertical transfer of heat in large-scale cloud systems, which, in turn, influences the jet shift. The researchers currently are further examining this and other possible mechanisms for how greenhouse gases and ozone influence the jet stream as well as Antarctic sea ice.
The results will appear in the Feb. 1 issue of the journal Science.
“Not only are the results of this paper important for better understanding climate change, but this paper is also important because it uses a new approach to try to better understand climate change; it uses observational data on a short time scale to try to look at cause and effect, which is something that is rarely done in climate research,” said Feldstein. “Also, our results are consistent with climate models, so this paper provides support that climate models are performing well at simulating the atmospheric response to ozone and greenhouse gases.”