Resolving the Paradox of the Antarctic Sea Ice

While
Arctic sea ice has been diminishing in recent decades, the Antarctic sea ice
extent has been increasing slightly. 
Researchers from the Georgia Institute of Technology provide an
explanation for the seeming paradox of increasing Antarctic sea ice in a
warming climate. The paper appears in the Early Edition of the Proceedings of
the National Academy of Science the week of August 16, 2010.

“We
wanted to understand this apparent paradox so that we can better understand
what might happen to the Antarctic sea ice in the coming century with increased
greenhouse warming,” said Jiping Liu, a research scientist in Georgia Tech’s School
of Earth and Atmospheric Sciences.

For
the last half of the 20th Century, as the atmosphere warmed, the
hydrological cycle accelerated and there was more precipitation in the Southern
Ocean surrounding Antarctica.  This
increased precipitation, mostly in the form of snow, stabilized the upper ocean
and insulated it from the ocean heat below. This insulating effect reduced the
amount of melting occurring below the sea ice. In addition, snow has a tendency to reflect atmospheric heat away from the
sea ice, which reduced melting from above.

However,
the climate models predict an accelerated warming exceeding natural variability
with increased loading of greenhouse gases in the 21st century. This
will likely result in the sea ice melting at a faster rate from both above and
below. Here’s how it works. Increased warming of the atmosphere is expected to
heat the upper ocean, which will increase the melting of the sea ice from
below. In addition, increased warming will also result in a reduced level of snowfall,
but more rain.  Because rain
doesn’t reflect heat back the way snow does, this will enhance the melting of
the Antarctic sea ice from above.

“Our
finding raises some interesting possibilities about what we might see in the
future. We may see, on a time scale of decades, a switch in the Antarctic,
where the sea ice extent begins to decrease,” said Judith A. Curry, chair of
the School of Earth and Atmospheric Sciences at Georgia Tech.

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