The Southern Hemisphere Double Whammy

CFC-caused, high-altitude ozone destruction occurs in both the Arctic and the Antarctic, but is much more pronounced in the Antarctic. In the Arctic, greenhouse gas warming is the main actor, but in the Antarctic, ozone loss adds a second protagonist, creating a double-whammy.

Since ozone absorbs sunlight in the UV-B portion of the spectrum, it warms the atmosphere around it. Thus, with the modern reduced levels of high-altitude ozone in the Antarctic, parts of the stratosphere are much cooler than before. Combined with greenhouse-gas warming to the north, the result is stronger, more-poleward, Antarctic Westerlies—the Antarctic Polar Vortex. These stronger Westerlies, unparalleled for at least the last 5,200 years, combined with greenhouse gas warming, yield a constellation of effects that contrast with those in the Arctic.

 Changes in wind global speeds (U). This plot shows the difference in annual average wind speeds around the globe between the periods 1996 to 2012 and 1979 to 1995. The dark red area just north of most the Antarctic coast, represents a 10% increase in wind speed. Plotted using  Climate Change Institute Climate Reanalyzer™ software .

Changes in wind global speeds (U). This plot shows the difference in annual average wind speeds around the globe between the periods 1996 to 2012 and 1979 to 1995. The dark red area just north of most the Antarctic coast, represents a 10% increase in wind speed. Plotted using Climate Change Institute Climate Reanalyzer™ software.

The stronger Antarctic Vortex means that the air inside it is colder than it would be if it was weaker. The colder air and stronger winds have resulted in increased amount of sea ice around much of the Antarctic coast line. The higher speeds of the Westerlies also brings more deep water to the surface, that is, more upwelling, which melts the ice shelves from their undersides. So, at the same time that we are observing record lows of Arctic sea ice, we see the record highs of coastal sea ice around Antarctica and record losses of Antarctic coastal ice shelves.

 Record low Arctic sea ice and record high Antarctic sea ice. October 11, 2012 “Two weeks after a new satellite era record was set in the Arctic Ocean for the least amount of sea ice coverage the ice surrounding Antarctica reached its annual winter maximum—and set a satellite era record for a new high.” From the  NASA Earth Observatory

Record low Arctic sea ice and record high Antarctic sea ice. October 11, 2012 “Two weeks after a new satellite era record was set in the Arctic Ocean for the least amount of sea ice coverage the ice surrounding Antarctica reached its annual winter maximum—and set a satellite era record for a new high.” From the NASA Earth Observatory

Just to the north of the westerlies, at the northern end of the Antarctic Peninsula, higher than usual temperatures occur due to greenhouse gas warming, just as they do in the Arctic, and record losses of both sea ice and ice shelves are being observed there. See the Antarctic Climate Change and the Environment report for research on Antarctic Westerlies and sea ice.

The effects of ozone-loss-caused changes in Antarctic wind patterns also extend to Australia where they are causing droughts in some regions, and to New Zealand and southern South America where they are increasing snowfall on the western slopes and causing some of the glaciers there to advance.

While the warmer-than-ice upwelling deep water is melting ice shelves, it is cooler than the greenhouse gas warmed air it meets at the ocean’s surface. Globally, this constant supply of cooler-than-air water at the surface, keeps the air temperatures of the southern hemisphere from increasing as much as those of the northern hemisphere, and keeps global average temperatures from rising as much as they would otherwise. Thus, ozone loss is masking the full effects of greenhouse gas warming just as industrial sulfate pollution did after the 1940s and before the Clean Air Act.

 Antarctic wind speeds and deepwater upwelling. Increased winds (left) result in increased upwelling of cold water (right) exposing more heat absorbing capacity to the surface. Plotted using  Climate Change Institute Climate Reanalyzer™ software.

Antarctic wind speeds and deepwater upwelling. Increased winds (left) result in increased upwelling of cold water (right) exposing more heat absorbing capacity to the surface. Plotted using Climate Change Institute Climate Reanalyzer™ software.

  Greenhouse gas warming in the Northern and Southern Hemispheres. The Southern Hemisphere, dominated as it is by oceans, and now also by increased upwelling, does not show as much increase in air temperature as the Northern Hemisphere. The ozone-loss-caused upwelling is masking the global average rise due to greenhouse gases. Plotted using   Climate Change Institute Climate Reanalyzer™ software.

Greenhouse gas warming in the Northern and Southern Hemispheres. The Southern Hemisphere, dominated as it is by oceans, and now also by increased upwelling, does not show as much increase in air temperature as the Northern Hemisphere. The ozone-loss-caused upwelling is masking the global average rise due to greenhouse gases. Plotted using Climate Change Institute Climate Reanalyzer™ software.