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Last Saturday, at the icy high point of the Greenland ice sheet, two miles in the sky and 500 miles above the Arctic Circle, something extraordinary happened: It rained for the first time.
Rain at a research station – not just a few drops or drizzle, but a stream flowing for several hours as temperatures rise slightly above freezing – is another troubling sign of the changing Arctic, which is warming faster than any other region on the planet. .
“It’s unbelievable because Greenland is writing a new chapter in the book,” said Marco Tedesco, a researcher at Columbia University’s Lamont-Doherty Earth Observatory. “This is really new.”
The station, called the Summit and occupied year-round under the auspices of the National Science Foundation, has had no rain records since observations began in the 1980s. Thomas Mote, a climate scientist at the University of Georgia, said computer simulations show no evidence going further back.
Conditions above the peak freezing point are almost equally rare. Martin Stendel, a senior researcher at the Danish Meteorological Institute, showed in an email message that before this century, ice cores have formed only six times in the last 2,000 years.
But in 2012, 2019, and this year’s Summit, temperatures above freezing have occurred—three times in less than 10 years.
The Greenland ice sheet, which is up to two miles thick and covers about 650,000 square miles, has been losing more ice in recent years as the Earth warms from man-made carbon dioxide and other emissions, contributing further to sea level rise. heat-trapping gases.
The surface of the ice sheet gains mass each year because snowfall accumulation is greater than surface melting. But in general, where the plate meets the ocean, it loses more ice as it melts and icebergs break. On average, over the past two decades, Greenland has lost more than 300 billion tons of ice each year.
This year will likely be an average year for surface buildup, he said. Pole PortalA website that disseminates the results of Danish Arctic surveys. Heavy snowfall earlier in the year suggested it could be an above-average year for accumulation, but two warming periods in July and early August changed that, causing widespread surface melting.
The warming that accompanied the rain last Saturday also caused more than 50 percent of the ice sheet surface to melt.
Dr. Mote said each of these meltdown events were “one-off” events. “But these events seem to be happening more and more often,” he said. “And that tells us we’re seeing real evidence of climate change in Greenland.”
Dr. Last Saturday, more than half of the surface melted in mid-August for the first time since satellite tracking began in 1979, Mote said. Normally the highest melting occurs in mid-July, as in 2012 when a major meltdown occurred.
“By mid-August, you usually see a rapid decline in melt activity and a drop in temperature,” he said.
Dr. Tedesco said the rain at Summit won’t directly contribute to sea level rise because water flows into the ice rather than the ocean. But if this is happening at the Summit, the impact at lower elevations will be more severe,” he said. “And this ice is actually going into the ocean.”
Dr. Tedesco described the rain at Summit as “worrying” because it indicates that even a little warming in the area could be effective.
“Half a degree of warming can really change the state of the Arctic because you can go from frozen to liquid,” he said. “That’s exactly what we’re seeing.”
Rain and meltdown last Saturday occurred as the jet stream descended south over northeastern Canada instead of flowing in its normal course from west to east. This brought the low-pressure air above the warmer waters, where it collected heat and moisture.
The jet stream then turned northward, bringing this air to southwest Greenland from where it passed over the ice sheet. Dr. Hot air and even the moisture-laden clouds themselves are causing temperatures to rise at Summit, causing precipitation to fall as rain instead of snow, Mote said.
Some scientists have attributed such jet stream interruptions, often called “ripples,” to climate change in the Arctic, but this is still a matter of debate. But they do happen, and they also create so-called blocking patterns that can stop high-pressure air over an area.
That’s what happened in earlier meltdown episodes this summer. The high-pressure air standing above the ice sheet led to clear skies that allowed more sunlight to reach the surface and melt more snow.
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