Is Antarctic ice sheet playing major role in Climate Change?
15 Dec 2016 11:49 PM GMT
The Antarctic Ice Sheet plays a major role in regional and global climate variability, a discovery that may help explain why sea ice in the southern hemisphere has been increasing despite the warming of the rest of the Earth, scientists say. Global climate models that look at the last several thousand years have failed to account for the amount of climate variability captured in the paleoclimate record, said researchers from Oregon State University (OSU) in the US.
Their hypothesis was that climate modelers were overlooking one crucial element in the overall climate system - an aspect of the ocean, atmosphere, biosphere or ice sheets - that might affect all parts of the system. “One thing we determined right off the bat was that virtually all of the climate models had the Antarctic Ice Sheet as a constant entity,” said Pepijn Bakker, former post-doctoral researcher at OSU.
“What we discovered, however, is that the ice sheet has undergone numerous pulses of variability that have had a cascading effect on the entire climate system,” said Bakker, who is now at the University of Bremen in Germany. The Antarctic Ice Sheet has demonstrated dynamic behaviour over the past 8,000 years, according to Andreas Schmittner, a climate scientist in OSU. “There is a natural variability in the deeper part of the ocean adjacent to the Antarctic Ice Sheet - similar to the Pacific Decadal Oscillation, or El Nino/La Nina but on a time scale of centuries - that causes small but significant changes in temperatures,” Schmittner said.
“When the ocean temperatures warm, it causes more direct melting of the ice sheet below the surface, and it increases the number of icebergs that calve off the ice sheet,” he said. Those two factors combine to provide an influx of fresh water into the Southern Ocean during these warm regimes, according to Peter Clark, from OSU. “The introduction of that cold, fresh water lessens the salinity and cools the surface temperatures, at the same time, stratifying the layers of water,” Clark said. “The cold, fresh water freezes more easily, creating additional sea ice despite warmer temperatures that are down hundreds of meters below the surface,” he said. The discovery may help explain why sea ice has expanded in the Southern Ocean despite global warming.
The same phenomenon does not occur in the Northern Hemisphere with the Greenland Ice Sheet because it is more landlocked and not subject to the same current shifts that affect the Antarctic Ice Sheet.
Hottest Arctic on record triggers massive ice melt
The Arctic shattered heat records in the past year, as unusually warm air triggered massive melting of ice and snow and a late fall freeze, US government scientists said today.
The grim assessment came in the Arctic Report Card 2016, a peer-reviewed report by 61 scientists around the globe that is issued by the National Oceanic and Atmospheric Administration.
The report spans from October 2015 to September 2016, a period when the Arctic’s “average annual air temperature over land areas was the highest in the observational record,” it said.
“Rarely have we seen the Arctic show a clearer, stronger or more pronounced signal of persistent warming and its cascading effects on the environment than this year,” said Jeremy Mathis, director of NOAA’s Arctic Research Program.
The Arctic region is continuing to warm up more than twice as fast as the rest of the planet, which is also expected to mark its hottest year in modern times.
Climate scientists say the reasons for the rising heat include the burning of fossil fuels which emit heat-trapping gases into the atmosphere, as well as the El Nino ocean warming trend, which ended mid-year but exacerbated the warming.
The Arctic’s annual air temperature over land was 3.5 degrees Celsius higher than it was in 1900.
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