Friday, 15 July 2016

Washington Post on Arctic ice melt


The extraordinary years have become the normal years’: Scientists survey radical Arctic melt


This July 13 image captured by a device on NASA’s Aqua satellite shows Franz Josef Land in the Arctic Ocean. (AFP/NASA)

13 July, 2016
A group of scientists studying a broad range of Arctic systems — from sea ice to permafrost to the Greenland ice sheet — gathered in D.C. Wednesday to lay out just how extreme a year 2016 has been so far for the northern cap of the planet.
I see the situation as a train going downhill,” said Marco Tedesco, who studies Greenland at the Lamont-Doherty Earth Observatory at Columbia University. “And the feedback mechanisms in the Arctic [are] the slope of your hill. And it gets harder and harder to stop it.”
The word “record” was uttered repeatedly at the event at the National Press Club, which was sponsored by SEARCH (the Study of Environmental Arctic Change). Walt Meier, a scientist with NASA who studies Arctic sea ice, laid out a series of “really extreme conditions” that began with sharply anomalous above-freezing temperatures at the North Pole for a short stint during the winter, and then led to large early breakups of ice above Alaska and in other regions. Overall, the Arctic sea ice extent has been at record lows for five out of six months so far this year.
We’ve lost about twice the size of the state of Alaska in terms of area,” said Meier, referring to the long-term trend in Arctic sea ice over the past several decades. “It’s also thinning as well, we’ve lost about 50 percent of the thickness. And this is happening more rapidly than even the most aggressive climate models.”
A series of researchers covering other Arctic systems then proceeded to tell very similar tales:
* For Greenland, April through June temperatures were about 3 degrees Celsius above the long-term average, said Tedesco — a new high. “The surface temperature set new records for April to June 2016,” he said. The peak moment for Greenland melting each year is right around now, and it isn’t clear whether the overall loss of water will match a staggering more than 500 billion tons in 2012, but it is already possible to say that “2016 is among the top years for melting,” Tedesco said.
* For Northern Hemisphere snow cover, the spring of 2016 set a new record low, said David Robinson, who runs the Rutgers University Global Snow Lab. “We lost the snow earlier than any time in record … throughout the Northern Hemisphere,” Robinson said.
* For thawing permafrost — carbon-packed soil layers that have the potential to spill even more greenhouse gases into the atmosphere as they warm — 2015 showed “record high temperatures” in measuring sites in Alaska, said Ted Schuur, who studies permafrost and wildfires at Arizona State University. But preliminary indicators, Shuur said, “point toward 2016 being a new record year.”
* For the Northern Hemisphere jet stream, which appears to be becoming more wavy and loopy in nature as the Arctic warms faster than the mid-latitudes, conditions in 2016 have once again been ripe for strange behavior, said Jennifer Francis, an Arctic researcher at Rutgers. “The difference in the temperature change between the Arctic and the mid-latitudes is at an all-time record high,” said Francis. “This is what we call Arctic amplification.”
The most troubling aspect of all of this, and a recurrent theme of the talks, was the researchers’ emphasis on how changes in the Arctic are not necessarily linear in nature as global warming grows — once you cross the freezing point, notes Robinson, it’s a total phase change for water, plain and simple — and that the system is laden with feedback processes, which amplify themselves.







(Rutgers University Global Snow Lab.)



Principal among those is a feedback involving the Earth’s albedo, or reflectivity. Less ice over Arctic waters, more meltwater atop Greenland and less snow on the land surface all darken the Earth and decrease its ability to reflect sunlight back to space. That means the energy stays around — causing more melting and warming.
Indeed, in a 2014 study, a team of scientists found that in the past three decades, the loss of Arctic sea ice has added 25 percent to the warming caused by carbon dioxide in the atmosphere.
All of this, and yet as the researchers repeatedly acknowledged, the truth is that 2016 is just one of several years showing extraordinary change in the fastest-warming part of the planet — 2012 still holds the record for the all-time low in Arctic sea ice extent and the all time maximum for Greenland melting, for instance. So it’s not so much that 2016 is so completely outside of all prior experience — but rather, that it’s yet another indicator of a new reality.
The extraordinary years have become the normal years,” said NASA’s Meier.


No comments:

Post a Comment