Something extraordinary occurred final Saturday at the frigid excessive level of the Greenland ice sheet, two miles in the sky and greater than 500 miles above the Arctic Circle: It rained for the first time.
The rain at a analysis station — not only a few drops or a drizzle however a stream for a number of hours, as temperatures rose barely above freezing — is yet one more troubling signal of a altering Arctic, which is warming sooner than another area on the planet.
“It’s incredible, because it does write a new chapter in the book of Greenland,” stated Marco Tedesco, a researcher at Lamont-Doherty Earth Observatory of Columbia University. “This is really new.”
At the station, which is known as Summit and is occupied year-round below the auspices of the National Science Foundation, there isn’t a document of rain since observations started in the 1980s. And laptop simulations present no proof going again even additional, stated Thomas Mote, a local weather scientist at the University of Georgia.
Above-freezing circumstances at Summit are practically as uncommon. Before this century, ice cores confirmed they’d occurred solely six instances in the previous 2,000 years, Martin Stendel, a senior researcher at the Danish Meteorological Institute, wrote in an e-mail message.
But above-freezing temperatures have now occurred at Summit in 2012, 2019 and this 12 months — 3 times in fewer than 10 years.
The Greenland ice sheet, which is as much as two miles thick and covers about 650,000 sq. miles, has been dropping extra ice and contributing extra to sea-level rise in current many years as the Earth has warmed from human-caused emissions of carbon dioxide and different heat-trapping gases.
The floor of the ice sheet positive aspects mass yearly, as a result of accumulation of snowfall is larger than floor melting. But total, the sheet loses extra ice via melting the place it meets the ocean, and thru the breaking-off of icebergs. On common over the previous twenty years, Greenland has misplaced greater than 300 billion tons of ice annually.
This 12 months will seemingly be a mean one for floor accumulation, stated Dr. Stendel, who can also be coordinator of Polar Portal, a web site that disseminates the outcomes of Danish Arctic analysis. Heavy snowfall early in the 12 months steered it could be an above-average 12 months for accumulation, however two durations of warming in July and one other in early August modified that by inflicting widespread floor melting.
The warming that accompanied the rain final Saturday additionally induced melting over greater than 50 p.c of the ice sheet floor.
Dr. Mote stated that these melting episodes have been every “one-off” occasions. “But these events seem to be happening more and more frequently,” he stated. “And that tells the story that we are seeing real evidence of climate change in Greenland.”
Last Saturday marked the first time since satellite tv for pc monitoring started in 1979 that melting has occurred over greater than half of the floor in mid-August, Dr. Mote stated. Normally peak melting happens in mid-July, because it did in 2012, when there was an enormous melting occasion.
“By the time you get to the middle of August, you’re usually seeing a rapid retreat of melt activity and a decline of temperature,” he stated.
Dr. Tedesco stated the rain at Summit wouldn’t contribute on to sea-level rise, as a result of the water drains into the ice quite than to the ocean. “But if this is happening at Summit, the effect at lower elevations will be more violent,” he stated. “And that ice is actually going to the ocean.”
Dr. Tedesco described the rain at Summit as “worrisome,” as a result of it exhibits that even somewhat warming can have an impact in the area.
“Half a degree of warming can really change the state of the Arctic because you can go from frozen to liquid,” he stated. “This is exactly what we’re seeing.”
The rain and melting final Saturday occurred when the jet stream, quite than flowing in its regular sample from west to east, dipped southward over northeastern Canada. That introduced low-pressure air over hotter waters, the place it picked up warmth and moisture.
The jet stream then looped again northward, bringing that air to southwestern Greenland from the place it swept over the ice sheet. The heat air and even the moisture-laden clouds themselves induced temperatures to rise at Summit and the precipitation to fall as rain quite than snow, Dr. Mote stated.
Some scientists have linked jet stream disruptions resembling this, also known as “waviness,” to local weather change in the Arctic, though that’s nonetheless a topic of debate. But they’re occurring, and are additionally creating so-called blocking patterns that may stall high-pressure air over a area.
That’s what occurred in the earlier melting episodes this summer time. High-pressure air that stalled over the ice sheet led to clear skies that allowed extra daylight to succeed in the floor, melting extra snow.