Warming Greenland ice sheet passes point of no return
Even if the climate cools, study finds, glaciers will continue to shrink


Date:
August 13, 2020
Source:
Ohio State University
Summary:
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.



FULL STORY ========================================================================== 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 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 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
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." This work was supported by grants from NASA. Other Ohio
State researchers who worked on this study are Salvatore Candela, Myoung
Noh and Adelaide Negrete.


========================================================================== Story Source: Materials provided by Ohio_State_University. Original
written by Laura Arenschield. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Michalea D. King, Ian M. Howat, Salvatore G. Candela, Myoung J. Noh,
Seonsgu Jeong, Brice P. Y. Noe"l, Michiel R. van den Broeke, Bert
Wouters, Adelaide Negrete. Dynamic ice loss from the Greenland Ice
Sheet driven by sustained glacier retreat. Communications Earth &
Environment, 2020; 1 (1) DOI: 10.1038/s43247-020-0001-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200813123550.htm

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