[D66] Greenland ice sheet passes point of no return

[R.O.]

VOOR DE DIPSHIT WEGKIJKER FLUKS:

August 13, 2020


  Warming Greenland ice sheet passes point of no return

by Laura Arenschield, The Ohio State University <http://www.osu.edu>

By
Laura Arenschield
phys.org
4 min
View Original 
<https://getpocket.com/redirect?url=https%3A%2F%2Fphys.org%2Fnews%2F2020-08-greenland-ice-sheet.html>

Icebergs near Greenland form from ice that has broken off--or 
calved--from glaciers on the island. A new study shows that the glaciers 
are losing ice rapidly enough that, even if global warming were to stop, 
Greenland's glaciers would continue to shrink. Credit: Michalea King

Nearly 40 years of satellite data from Greenland shows that glaciers on 
the island have shrunk so much that even if global warming were to stop 
today, the ice sheet would continue shrinking.

The finding, published today, Aug. 13, in the journal /Nature 
Communications Earth and Environment/, means that Greenland's glaciers 
have passed a tipping point of sorts, where the snowfall that 
replenishes the ice sheet <https://phys.org/tags/ice+sheet/> each year 
cannot keep up with the ice that is flowing into the ocean from glaciers.

"We've been looking at these remote sensing observations to study how 
ice discharge and accumulation have varied," said Michalea King, lead 
author of the study and a researcher at The Ohio State University's Byrd 
Polar and Climate Research Center. "And what we've found is that the ice 
that's discharging into the ocean is far surpassing the snow that's 
accumulating on the surface of the ice sheet."

King and other researchers analyzed monthly satellite data from more 
than 200 large glaciers draining into the ocean around Greenland. Their 
observations show how much ice breaks off into icebergs or melts from 
the glaciers into the ocean. They also show the amount of snowfall each 
year—the way these glaciers get replenished.

The researchers found that, throughout the 1980s and 90s, snow gained 
through accumulation and ice melted or calved from glaciers were mostly 
in balance, keeping the ice sheet intact. Through those decades, the 
researchers found, the ice sheets generally lost about 450 gigatons 
(about 450 billion tons) of ice each year from flowing outlet glaciers, 
which was replaced with snowfall.

"We are measuring the pulse of the ice sheet—how much ice glaciers drain 
at the edges of the ice sheet—which increases in the summer. And what we 
see is that it was relatively steady until a big increase in ice 
discharging to the ocean during a short five- to six-year period," King 
said.

The researchers' analysis found that the baseline of that pulse—the 
amount of ice being lost each year—started increasing steadily around 
2000, so that the glaciers were losing about 500 gigatons each year. 
Snowfall did not increase at the same time, and over the last decade, 
the rate of ice loss from glaciers has stayed about the same—meaning the 
ice sheet has been losing ice more rapidly than it's being replenished.

"Glaciers have been sensitive to seasonal melt for as long as we've been 
able to observe it, with spikes in ice discharge in the summer," she 
said. "But starting in 2000, you start superimposing that seasonal melt 
on a higher baseline—so you're going to get even more losses."

Before 2000, the ice sheet would have about the same chance to gain or 
lose mass each year. In the current climate, the ice sheet will gain 
mass in only one out of every 100 years.

King said that large glaciers across Greenland have retreated about 3 
kilometers on average since 1985—"that's a lot of distance," she said. 
The glaciers have shrunk back enough that many of them are sitting in 
deeper water, meaning more ice is in contact with water. Warm ocean 
water melts glacier ice, and also makes it difficult for the glaciers to 
grow back to their previous positions.

That means that even if humans were somehow miraculously able to stop 
climate change in its tracks, ice lost from glaciers draining ice to the 
ocean <https://phys.org/tags/ocean/> would likely still exceed ice 
gained from snow accumulation, and the ice sheet would continue to 
shrink for some time.

"Glacier retreat has knocked the dynamics of the whole ice sheet into a 
constant state of loss," said Ian Howat, a co-author on the paper, 
professor of earth sciences and distinguished university scholar at Ohio 
State. "Even if the climate were to stay the same or even get a little 
colder, the ice sheet would still be losing mass."

Shrinking glaciers <https://phys.org/tags/glaciers/> in Greenland are a 
problem for the entire planet. The ice that melts or breaks off from 
Greenland's ice sheets ends up in the Atlantic Ocean—and, eventually, 
all of the world's oceans. Ice from Greenland is a leading contributor 
to sea level rise—last year, enough ice melted or broke off from the 
Greenland ice sheet to cause the oceans to rise by 2.2 millimeters in 
just two months.

The new findings are bleak, but King said there are silver linings.

"It's always a positive thing to learn more about glacier environments, 
because we can only improve our predictions for how rapidly things will 
change in the future," she said. "And that can only help us with 
adaptation and mitigation strategies. The more we know, the better we 
can prepare."


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tuxtown.net/pipermail/d66/attachments/20200815/1a8994e8/attachment.html>