Southern hemisphere wind speed trends cause aerosol forcing over last two decades
Observations indicate that the westerly jet in the southern hemisphere troposphere is accelerating. Using a global aerosol model we estimate that the increase in wind speed of 0.45±0.2 m/s/decade at 50–65 S since the early 1980s caused a higher sea spray flux, resulting in an increase of cloud condensation nucleus concentrations of more than 85% in some regions, and of 22% on average between 50 and 65 S. These fractional increases are the same order of those over many northern hemisphere land areas due to changes in air pollution over the same period. The changes in cloud drop concentration cause an increase in cloud reflectivity and a radiative forcing at 50–65 S comparable in magnitude but acting against that from greenhouse gas forcing over the same time period, and thus represent a substantial negative climate feedback. However, recovery of Antarctic ozone depletion in the next two decades will likely cause a fall in wind speeds, a decrease in cloud drop concentration and a corresponding positive cloud feedback.
This paper by Korhonen et al. appeared in GRL.
http://www.agu.org/pubs/crossref/2010/2009GL041320.shtml
It was widely picked up by the media, such as in the Scotsman, the New York Times and National Geographic
The tone of these reports was that repair of the ozone hole might be a bad thing. This is not what we intended to point out. The repair of the ozone hole is certainly a good thing, but we should understand that there will be feedbacks in the climate system as a consequence. Some of these feedbacks have been highlighted by others (see the reference list in our paper). We have now shown that changes in clouds also need to be considered. If we are correct, then slower wind speeds between 50 and 65 S in future could cause a positive radiative forcing
A related assessment, which came out just before our publication, is the Scientific Committee on Antarctic Research (SCAR) report. The NERC Planet Earth magazine reported Ozone hole has shielded Antarctica from global warming
It’s important to understand the limits of our study. We are not saying that the ozone hole has mitigated the warming over Antarctica. The effect of the increased winds is to cause a negative cloud radiative forcing (cooling) limited to between 50 and 65 degrees south (and would cause a warming when the ozone hole recovered). We’d need to study the cloud impact in a fully coupled climate model to understand wider geographical impacts and feedbacks.