A new NASA-funded study finds that predicted increases inprecipitation due to warmer air temperatures from greenhouse gasemissions may actually increase sea ice volume in the Antarctic’sSouthern Ocean. This adds new evidence of potential asymmetry betweenthe two poles, and may be an indication that climate change processesmay have different impact on different areas of the globe.
"Most people have heard of climate change and how rising airtemperatures are melting glaciers and sea ice in the Arctic," saidDylan C. Powell, co-author of the paper and a doctoral candidate at theUniversity of Maryland-Baltimore County. "However, findings from oursimulations suggest a counterintuitive phenomenon. Some of the melt inthe Arctic may be offset by increases in sea ice volume in theAntarctic.
The researchers used satellite observations for the first time,specifically from the Special Sensor Microwave/Imager, to assess snowdepth on sea ice, and included the satellite observations in theirmodel. As a result, they improved prediction of precipitation rates. Byincorporating satellite observations into this new method, theresearchers achieved more stable and realistic precipitation data thanthe typically variable data found in the polar regions. The paper waspublished in the June issue of the American Geophysical Union's Journalof Geophysical Research.
"On any given day, sea ice cover in the oceans of the polar regionsis about the size of the U.S.," said Thorsten Markus, co-author of thepaper and a research scientist at NASA’s Goddard Space Flight Center,Greenbelt, Md. "Far-flung locations like the Arctic and Antarcticactually impact our temperature and climate where we live and work on adaily basis."
According to Markus, the impact of the northernmost and southernmostparts on Earth on climate in other parts of the globe can be explainedby thermohaline circulation – the movement of ocean water that iscaused by temperature and salinity variations in the ocean. Throughthis process, ocean circulation acts like a heat pump and determinesour climate to a great extent. The deep and bottom water masses of theoceans make contact with the atmosphere only at high latitudes near orat the poles. In the polar regions, the water cools down and releasesits salt upon freezing, a process that also makes the water heavier.The cooler, salty, water then sinks down and cycles back towards theequator. The water is then replaced by warmer water from low andmoderate latitudes, and the process then begins again.
Typically, warming of the climate leads to increased melting ratesof sea ice cover and increased precipitation rates. However, in theSouthern Ocean, with increased precipitation rates and deeper snow, theadditional load of snow becomes so heavy that it pushes the Antarcticsea ice below sea level. This results in even more and even thicker seaice when the snow refreezes as more ice. Therefore, the paper indicatesthat some climate processes, like warmer air temperatures increasingthe amount of sea ice, may go against what we would normally believewould occur.
"We used computer-generated simulations to get this research result.I hope that in the future we’ll be able to verify this result with realdata through a long-term ice thickness measurement campaign," saidPowell. "Our goal as scientists is to collect hard data to verify whatthe computer model is telling us. It will be critical to know forcertain whether average sea ice thickness is indeed increasing in theAntarctic as our model indicates, and to determine what environmentalfactors are spurring this apparent phenomenon."
Achim Stossel of the Department of Oceanography at Texas A&MUniversity, College Station, Tex., a third co-author on this paper,advises that "while numerical models have improved considerably overthe last two decades, seemingly minor processes like the snow-to-iceconversion still need to be better incorporated in models as they canhave a significant impact on the results and therefore on climatepredictions."
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