Sunday, January 10, 2010

Ozone hole drive rapid changes

One finding from recent years that received prominence in the SCAR report concerned the effects of the ozone hole on the Antarctic climate.

Unlike the coastal areas, particularly in West Antarctica, the interior of Antarctica has cooled slightly, according to polar researchers cited in the SCAR report. That’s because the ozone hole over the Southern Hemisphere has cooled the stratosphere, the layer of the atmosphere above the troposphere that people inhabit.

However, the ocean around the continent and regions to the north are warming. The temperature differential has caused atmospheric circulation to intensify around Antarctica, effectively shielding much of the continent from the intrusion of warmer air to the north.

But as the ozone hole heals, those westerly winds will ease, allowing warmer air to mix more easily into the Antarctic atmosphere. The SCAR report estimates a continent-wide temperature increase of 3 degrees Celsius by 2100.

“This is what has happened in the northern hemisphere. You have a relatively warm Arctic and a warm low- to mid-latitudes, and the westerlies have slowed down,” Mayewski said. “The big questions for the Antarctic are when it will happen and how fast will it happen.”

Mayewski said based on climate records, particularly from ice cores, that sudden shifts in position and strength of the westerlies have created many of the abrupt climate changes of the past.
Mayewski said: “The implicit but not explicit statement in my mind in this report is the fact that we could very well be headed for not a linear change in the westerlies, but an abrupt change in the westerlies,” he said. “If we experience a very abrupt weakening of the westerlies — we can show that it happened in the past — we could very well have accelerated levels of warming in Antarctica.”

A recent paper in the journal Geophysical Research Letters by Marco Tedesco at City College of New York and Andrew Monaghan at the National Center for Atmospheric Research in Boulder, Colo., suggested that a 30-year record low in Antarctic snowmelt during the 2008-09 austral summer was likely due to intensified westerlies and El NiƱo-Southern Oscillation (ENSO). ENSO is a periodic change in oceanic and atmospheric conditions in the tropical Pacific Ocean that has far-reaching effects on weather around the world.


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