Arctic Greens While Antarctic Ice Grows
01 April, 2013
An AFP report  carried by ABC Science said:
In the coming decades, global warming will cause grass, shrubs and trees to thrive in Arctic soil stripped of ice and permafrost, while sea ice around Antarctica will grow, according to a computer simulations published in the journal Nature Climate Change published on April 1, 2013.
Wooded areas in the Arctic could increase by as much as 52 percent by the 2050s as the so-called tree line - the maximum latitude at which trees can grow - shifts hundreds of kilometers north, according to the research.
The report said:
Arctic has become one of the world's 'hotspots' for global warming. Over the past quarter-century, temperatures there have been rising roughly twice as fast as in the rest of the world.
The report quoted Dr Richard Pearson of the American Museum of Natural History's Center for Biodiversity and Conservation: "Such widespread redistribution of Arctic vegetation would have impacts that reverberate through the global ecosystem."
"These impacts would extend far beyond the Arctic region," says Pearson. "For example, some species of birds seasonally migrate from lower latitudes and rely on finding particular polar habitats, such as open space for ground-nesting."
In a separate study, published in the journal Nature Geoscience, Dutch scientists report that ice shelves in Antarctica - another part of the climate equation - have in fact been growing thanks to global warming.
Meltwater that runs off the Antarctic mainland provides a cold, protective "cap" for ice shelves because it comes from freshwater, which is denser than seawater, the team from the Royal Netherlands Meteorological Institute say.
Ice shelves are the floating blankets of ice that extend from the coast. They are fed by glaciers that move ice down from the ice sheet and towards the sea.
The study found:
The freshwater acts as a cold coating for the underside of the ice shelf and cocoons it from warmer seas. This would explain an apparent anomaly: why sea ice around Antarctica has been growing, reaching the greatest-ever recorded extent in 2010, it suggests.
Other scientists, asked to comment on the work, concurred that the phenomenon, if confirmed, was one of several unexpected impacts from global warming, a hugely complex interplay of land, sea and air.
"This is a major, new piece of work with wide implications for assessing Antarctica's ice mass in the coming decades," says palaeo-climatologist Dr Valerie Masson-Delmotte of France's Laboratory for Climate and Environmental Science (LCSE).
She points to a worrying rise in sea levels in 2011 and 2012, due partly to expansion of the ocean through warming and through glacier runoff, coming from mountains and also from Greenland and Antarctica, the two biggest sources of land ice on the planet.
Citing the study Reuters’ Environment Correspondent Alister Doyle reported  from Oslo:
The extent of sea ice around Antarctica in winter is expanding, a paradoxical shift caused by cold plumes of summer melt water that re-freeze fast when temperatures drop.
The study found:
An increasing summer thaw of ice on the edges of Antarctica, twinned with less than expected snowfall on the frozen continent, is also adding slightly to sea level rise.
Climate scientists have been struggling to explain why sea ice around Antarctica has been growing, reaching a record extent in the winter of 2010, when ice on the Arctic Ocean at the other end of the planet shrank to a record low in 2012.
"Sea ice around Antarctica is increasing despite the warming global climate," said Richard Bintanja, lead author of the study at the Royal Netherlands Meteorological Institute.
"This is caused by melting of the ice sheets from below," he told.
Ice is made of fresh water and, when ice shelves on the fringes of Antarctica thaw in summer because of upwellings of warming sea water, the melt water forms a cool layer that floats on the denser, warmer salty sea water below, the study said. In winter, the melt water readily turns to ice because it freezes at zero degrees Celsius, above sea water at -2C (28.4F).
At a winter maximum in September, ice on the sea around Antarctica covers about 19 million sq kms (7.3 million sq miles), bigger than Antarctica's land area. It then melts away into the ocean as summer approaches.
Among other scientists, Paul Holland of the British Antarctic Survey stuck to his findings last year that a shift in winds linked to climate change was blowing a layer of melt water further out to sea and adding to winter ice.
"The possibility remains that the real increase is the sum of wind-driven and melt water-driven effects, of course. That would be my best guess, with the melt water effect being the smaller of the two," he said.
Bintanja's study also said the cool melt water layer may limit the amount of water sucked from the oceans that falls as snow on Antarctica. Cold air can hold less moisture than warm.
"Cool sea surface temperatures around Antarctica could offset projected snowfall increases in Antarctica, with implications for estimates of future sea-level rise," it said.
The U.N. panel of climate scientists has estimated that sea levels will rise by between 18 and 59 cm (7-24 inches) this century, more if thaws of Antarctica and Greenland accelerate. The panel's main scenarios assume that Antarctica alone will make sea levels fall by between 2 and 14 cms this century because more snowfall will extract water from the sea.
But the cited study said that Antarctica was losing about 250 billion metric tons of ice a year - equivalent to 0.07 millimeter (0.003 inch) of sea level rise a year, Bintanja said. "Antarctic mass loss seems to be accelerating," it said.
Another study in Nature Geoscience said Antarctica's snowfall had been over-estimated by between 11 and 36.5 billion metric tons a year because of fierce winds blasting many regions.
Strong winds created conditions to "sublimate" snow, or make it pass from a frozen state to a gas without first becoming liquid, a US-led team wrote.
 April 1, 2013 “Arctic to green as Antarctic sea ice grows”,
 March 31, 2013 “Global warming means seas freeze more off Antarctica: study”,
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