Wednesday, November 21, 2012

NASA: Antarctic sea ice grows – but the climate’s still changing

Sheldon Glacier, Antarctica with Mount Barre in background,
from Ryder Bay near Rothera Research Station, Adelaide Island.
A new study examines why Antarctic sea ice cover has increased under the effects of climate change over the past two decades.

A NASA study has reported a rise in Antarctic sea ice.
For cherry picking climate change deniers, it may be a neat counterweight to Arctic ice melt but, as the NASA study shows, Antarctic ice expansion is another worrying trend in global climate change.
The principal finding of the new NASA study, conducted in conjunction with the British Antarctic Study, relates to a significant growth in Antarctic sea ice drift caused by changes in the wind currents around Antarctica observed over the past twenty years.
Changes in wind currents can arise due to an alteration in underlying sea temperatures and it is here that the rapid ice loss seen in the Arctic Ocean may be reconciled with what would appear, at first glance, to be conflicting data from the Antarctic.

The sea ice in the Arctic Ocean dropped below the previous all-time record set in 2007.
This year also marks the first time that there has been less than 4 million square kilometers (1.54 million square miles) of sea ice since satellite observations began in 1979.
This animation shows the 2012 time-series of ice extent using sea ice concentration data from the DMSP SSMI/S satellite sensor.
The black area represents the daily average (median) sea ice extent over the 1979-2000 time period.
Layered over top of that are the daily satellite measurements from January 1 -- September 14, 2012.
A rapid melt begins in July, whereby the 2012 ice extents fall far below the historical average.
The National Snow and Ice Data Center will confirm the final minimum ice extent data and area once the melt stabilizes, usually in mid-September.

In mid-October Digital Journal reported on the record ice melt of Arctic sea ice observed by NASA which now has comparative data on the Arctic polar ice cap dating back almost 35 years.
According to NASA and the British Antarctic Survey, the expansion of Antarctic sea ice is but another facet of climate change, connected to rather than conflicting with the opposite effect observed in the Arctic.
Using maps created by NASA’s Jet Propulsion Laboratory (JPL) which have been built up from five million individual daily measurements of the flows of sea ice around the Antarctic continent, research scientists Ron Kwok of JPL and Paul Holland of the Natural Environment Research Council's British Antarctic Survey, Cambridge, United Kingdom have constructed a model to illustrate what is happening in the Antarctic.
For the first time, researchers have been able to show long term changes in the Antarctic sea ice over a period of almost two decades using data collected by four U.S. Defense Meteorological satellites.
Said Holland, the principal author of the report recently published in Nature Geosciences,
“Until now these changes in ice drift were only speculated upon, using computer models of Antarctic winds. This study of direct satellite observations shows the complexity of climate change. The total Antarctic sea-ice cover is increasing slowly, but individual regions are actually experiencing much larger gains and losses that are almost offsetting each other overall. We now know that these regional changes are caused by changes in the winds, which in turn affect the ice cover through changes in both ice drift and air temperature. The changes in ice drift also suggest large changes in the ocean surrounding Antarctica, which is very sensitive to the cold and salty water produced by sea-ice growth.
“Sea ice is constantly on the move; around Antarctica the ice is blown away from the continent by strong northward winds. Since 1992 this ice drift has changed. In some areas the export of ice away from Antarctica has doubled, while in others it has decreased significantly.”
It is significant that whereas the headline figure is reporting a growth in Antarctic sea ice, Holland refers to this being a two-way flow with expansion of sea ice in some areas being offset by losses of ice elsewhere in seas around Antarctica.
The northward drift of sea ice could help explain extremes of sea ice growth in some areas of the Southern Ocean around the Antarctic continent by means of a cooling feedback reaction.
Sea ice, being white, is highly reflective of the sun’s rays whilst dark sea water in liquid form absorbs heat from the sun.
Thus, expanding sea ice can cause a cooling effect encouraging the formation of more sea ice around itself.
The reflective qualities of sea ice means that it plays a significant role in Earth’s environment, not only reflecting heat from the sun back into space but forming a niche habitat for a variety of marine species.
At both the North and South polar regions, sea ice reaches its minimum in late summer after months when the polar regions are bathed in 24 hour sunlight.
In the Arctic, however, the trend for these summer sea ice minima has been inexorably downwards, so much so that scientists now predict that the Arctic Ocean will be free of sea ice during the summer before the end of the 21st century.
During Antarctica’s winter freeze, sea ice generally expands and covers an area of the ocean around the polar continent approximately twice the size of Europe.
The sea ice, as well as reflecting sunlight, also acts as a blanket insulating the relatively warm seawater beneath from the sub zero temperatures in the air above.
Again, changes in the sea ice, with its reflective and insulating qualities, are likely to have unpredictable consequences for the Antarctic continent and, flowing from that, climate change globally.
JPL/British Antarctic Survey says the new study helps in understanding why there should be such a contrast between the two polar regions when it comes to sea ice.
While the Arctic appears to be melting at an accelerating rate, over the period of the study, Antarctic sea ice in toto has actually increased, albeit slightly.
The researchers state, however, that the slight net Antarctic increase in sea ice hides the underlying story of large regional increases and decreases, significant localised changes which are wind-driven. The different topography of the Arctic Ocean and Antarctica also provides some clues as to what is happening, scientists say.
Whereas the Arctic Ocean is, to all intends and purposes, surrounded by land so that wind flows cannot cause Arctic ice to expand in the same way, in Antarctica and the Southern Ocean, northward winds, blowing off the continent, can force sea ice to ‘flow’ northwards as there are no land or continental barriers to halt the flow.
Highlighting how any localised expansion of Antarctic sea ice cannot be seen in isolation, Ron Kwok of JPL says,
“The Antarctic sea ice cover interacts with the global climate system very differently than that of the Arctic, and these results highlight the sensitivity of the Antarctic ice coverage to changes in the strength of the winds around the continent."
Wind driven flows of sea ice around Antarctica
Wind driven flows of sea ice around Antarctica
NASA- JPL/ British Antarctic Survey

 From the National Snow and Ice Data Center:
Animated map of 2012 sea ice extent shown side-by-side with 1979--2009 climatology.

The NASA/British Antarctic Survey report emphasises that it focused on sea ice flows and formation around the Antarctic which has to be distinguished from the land-based Antarctic Ice Sheet, glacial ice, which continues to lose volume.
Although not touched on by the report, the wind induced changes in sea ice formation around the Antarctic could result in some glacial ice which would otherwise be ‘locked-in’ by sea ice, tending to calf icebergs which might not otherwise have floated off from the continental ice sheet.
Elsewhere, expansion of sea ice could have as yet unforeseen localised effects on the climate.
As with all climate change studies and models, due to the timescales involved in assembling meaningful data, knowing what may happen is fraught with difficulty whilst unfulfilled predictions merely serve to provide ammunition to those who would hold that climate change is a myth.
The NASA/British Antarctic Survey study does not attempt to predict what the future may hold, but, just as it is unnecessary to count the spots on a leopard to identify it as a big cat, the study is yet another indication that climate change is here and now, even if some politicians think it’s a pussycat.

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