According to professor of meteorology Sukyoung Lee, this finding has implications for the wellbeing of the planet, and the wellness of its inhabitants worldwide, because ‘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.’
Lee said that though it was already thought that both ozone depletion and greenhouse gas increase have contributed to the southward shift of the Southern Hemisphere jet stream, until now, no one has been able to use observational data to determine the extent to which each has contributed to the shift. ‘Understanding the differences between these two forcings is important in predicting what will happen as the ozone hole recovers,’ she explained. ‘The jet stream is expected to shift back toward the north as ozone is replenished, yet the greenhouse-gas effect could negate this.’
With her colleague Steven Feldstein, professor of meteorology, Lee developed a new method to distinguish between the effects of the two forcings, using a cluster analysis to investigate the effects of ozone and greenhouse gas on four different observed wind patterns. The results, which appear in the journal Science, were that the first wind pattern, which corresponded to an equatorward shift of the midlatitude westerlies, was associated with greenhouse gases, whilst the third pattern, which corresponded to a poleward shift of the westerlies, was associated with ozone. They found that the other two wind patterns were unrelated to either of the forcings, but a long-term decline in the frequency of the first pattern and a long-term increase in the frequency of the third pattern could explain the changes in the Southern Hemisphere jet stream.
Feldstein concluded, ‘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. 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.’