Why is Antarctic sea ice area not decreasing despite global warming?

Antarctic sea ice extent (area) has been increasing. But the mass, the total amount of ice, is decreasing, because the ice is becoming thinner. See the next post.

http://www.theguardian.com/environment/2014/oct/09/why-is-antarctic-sea-ice-at-record-levels-despite-global-warming

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But Dr Claire Parkinson, a senior scientist at Nasa’s Goddard Space Flight Centre, says increasing Antarctic ice does not contradict the general warming trend. Overall the Earth is losing sea ice at a rate of 35,000 sq km per year (13,514 sq miles).

“Not every location on the Earth is having the same responses to climate changes. The fact that ice in one part of the world is doing one thing and in another part ice is doing another is not surprising. The Earth is large and as the climate changes it is normal to see different things going on,” says Parkinson.

In a video made by Eco Audit reader and journalist Fraser Johnston, Dr Guy Williams, a sea ice scientist at the Tasmanian Institute for Marine and Antarctic Studies (Imas), says that even though it had fooled climate models the increasing sea ice was well understood by scientists.

“In some ways it’s a bit counterintuitive for people trying to understand how global warming is affecting our polar regions, but in fact it’s actually completely in line with how climate scientists expect Antarctica and the Southern Ocean to respond. Particularly in respect to increased winds and increased melt water,” said Williams.

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Currently, the effect of greenhouse gases is being overshadowed by other local climate phenomena, says Turner. “By far the biggest impact has been the ozone hole. The signal of increasing greenhouse gases is buried beneath all the other signals.”

The depletion of the ozone layer above Antarctica during last century by emissions of chlorofluorocarbons (CFCs) has caused an overall cooling trend on the continent.

Ozone itself is a greenhouse gas and its reduction has seen more heat reflecting back into space. Although the ozone hole has begun to show the first signs of recovery, levels are still significantly reduced. Parkinson says the loss of ozone is probably the second largest human impact on global climate after carbon dioxide.

One of the effects of ozone loss on the Antarctic has been the increasing frequency and ferocity of winds and storms around the continent. According to Turner, ozone depletion has caused winds in the Southern Ocean to increase by 15-20%. In particular, the cooling trend may have caused a low pressure system in the Amundsen sea to increase in intensity or frequency.

This vortex sucks air from the frozen inside of the continent and it rushes out over the Ross Sea to the west. This is where 80% of Antarctica’s ice expansion has occurred.

The effect of the intensifying winds is coupled with a massive dump of cold, fresh water into the Ross Sea from the Pine Island glacier. This water, which floats on the surface, is less dense, colder and freezes more easily than the sea water below, and when it is struck by storm winds from the continent it forms ice floes.

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Sea ice in Antarctica is very different to its northern counterpart. In the south, ice melts away almost completely every year. The new ice produced each year is thinner and more volatile than the older more stable ice in the Arctic. These large fluctuations, said Turner, meant the “input” of greenhouse gases was not yet the dominant force in the region’s climate.

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