After warming fast, part of Antarctica gets a chill: study


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Icebergs grind against the shallows off the Rothera base, run by the British Antarctic Survey, on the Antarctic Peninsula Icebergs grind against the shallows off the Rothera base, run by the British Antarctic Survey, on the Antarctic Peninsula


The Antarctic Peninsula, among the fastest warming places on Earth last century, has since cooled due to natural swings in the local climate, scientists said on Wednesday, adding that the respite from the thaw is likely to be brief.
Rapid warming until the late 1990s on the peninsula, which snakes up toward South America, triggered the break-up of ancient ice shelves, which are vast expanses of ice floating on the sea at the end of glaciers, and declines in some penguin colonies.
But a shift to colder winds and more sea ice since then have brought a chill to the region despite the build-up of greenhouse gases in the atmosphere, the scientists wrote in the journal Nature.
"The increase of greenhouse gases ... is being overwhelmed in this part of the Antarctic" by natural variations in the local climate, said lead author John Turner of the British Antarctic Survey (BAS).
"We're certainly not saying that global warming has stopped. On the contrary," he told a telephone news conference on the study. "We're highlighting the complexity of climate change."
Since about 1998, local air temperatures have fallen about 0.5 degree Celsius (0.9 Fahrenheit) a decade, roughly the rate at which they had previously been warming since about 1950.
Stabilization of the ozone hole over Antarctica, which shields the planet from ultra-violet rays and has been damaged by man-made chemicals, may partly explain the shift in winds that led to the cooling, the study said.
But the build-up of greenhouse gases, mainly from the global burning of fossil fuels, means the cooling may be just a blip in a corner of Antarctica. Temperatures were likely to start rising again and could gain by 3-4C (5.4-7.2F) by 2100, Turner said.
At a Paris summit in December, almost 200 governments agreed the strongest deal yet to rein in global warming, aiming to phase out fossil fuels by 2100. U.S. Republican presidential nominee Donald Trump, who does not believe in man-made warming, says he would pull out if elected.
On the Antarctic Peninsula, about 10 ice shelves, from the Jones to the Wilkins, have retreated sharply or disintegrated in recent decades.
The day after
The splintering of the Larsen B ice shelf in 2002 inspired the opening scene of a Hollywood disaster movie about climate change, "The Day After Tomorrow", where a vast crack destroys a U.S. scientific camp.
In the real world, the worry is that far bigger ice shelves further south in Antarctica will also break up, allowing vast glaciers to slide more quickly into the sea and add to a rise in ocean levels.
Wednesday's study "begs a question as to the climate variability in other regions of Antarctica - where there is far more ice with the potential to melt and cause sea-level rise - as well as in the Arctic and other locations," Martin Siegert, an expert at Imperial College, London, wrote in a comment.
And on the Antarctic Peninsula, in 2014 scientists spotted a new crack tens of kms (miles) long on the Larsen C ice shelf.
"The future of the Larsen C is in the balance," said David Vaughan, director of science at BAS, adding it had probably not yet reached a point of no return.
Some other scientists said a rise in ocean temperatures that are gnawing away at Antarctica's icy coastline from below was more important for sea level rise than the air temperatures studied by Turner.
"The real threat is ocean warming," said Andrew Shepherd of the University of Leeds.

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