Greenland ice sheet shows losses in 2019

Date:
August 20, 2020
Source:
GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre
Summary:
The Greenland Ice Sheet recorded a new record loss of mass in
2019. This was the finding of a team of international researchers
after evaluating data from satellite observations and modelling
data.



FULL STORY ==========================================================================
The Greenland Ice Sheet recorded a new record loss of mass in 2019. This
was the finding of a team of international researchers after evaluating
data from satellite observations and modelling data. The total loss
amounted to 532 billion metric tons, more than in the previous record
year 2012 (464 billion metric tons), which equates to an average global sea-level rise of 1.5 mm.

After two years characterised by low loss of mass in 2017 and 2018, the
ice sheet is now heading toward increasing mass losses. The five years
with the greatest losses all occurred in the last decade. The ice loss
in 2019 exceeded the increase due to snowfall by over 80%. The study
was published today in the journal Communications Earth & Environment.


==========================================================================
In order to determine the ice loss, researchers from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), the
German Research Centre for Geosciences GFZ and international partners
evaluated satellite data from the GRACE mission, and its successor
mission, GRACE Follow- On (GRACE-FO). The satellites provided highly
accurate measurements, which were used to create monthly maps of Earth's gravity. The redistribution of the masses, e.g. ice losses in the oceans,
leads to temporal and spatial changes in Earth's gravitational forces. The researchers compared the satellite data with regional climate models
that are specially designed to calculate the snowfall and the melting
of the ice sheet.

"After a two-year 'breather', in 2019 the mass loss increased steeply
and exceeded all annual losses since 1948, and probably for more than
100 years," says Ingo Sasgen, a glaciologist at the AWI in Bremerhaven
and first author of the study. "There are increasingly frequent, stable high-pressure areas over the ice sheet, which promote the influx of warm
air from the middle latitudes.

We saw a similar pattern in the previous record year 2012." The mass
balance for a given a year is calculated using the difference between
the ice increase due to snowfall and ice loss due to melting and ice
discharge at the edge of the ice sheet. "The snowfall in 2019 was below
the long-term average, and that also contributed to the record figure," explains Marco Tedesco, a professor at Columbia University and co-author
of the study. "By comparing satellite data with regional climate models,
we were able to see precisely which processes were involved and to what
extent, and which general weather conditions were dominant," he adds.

The two satellite missions GRACE and GRACE-FO, which monitor the Earth's gravitational field, play a vital role in the continuous observations of
the Greenland Ice Sheet. The measurements allow the mass changes in the
ice sheet to be quantified. "The GRACE satellite mission, which ended in
summer 2017, provided us with essential data on ice loss in the polar
regions over a period of 15 years," explains Christoph Dahle from the
GFZ, who is responsible for calculating the gravitational fields from
the mission's raw data. "After a gap of about a year, in summer 2018 we
were able to resume monitoring with the follow-on mission, GRACE-FO."
In summer, the Arctic warms roughly one and a half times as quickly
as the global average. Added to this are the various feedback effects
that increase the ice loss. "2017 and 2018 were very cold years in
Greenland, with high snowfall," says Sasgen. The GRACE/GRACE-FO data
shows, however, that in these years the mass balance was negative due to
the high discharge from the glacier into the ocean. "We see substantial variations from year to year. But the five years with the highest losses
since 1948 were all in the last decade," reports Sasgen.


========================================================================== Story Source: Materials provided by GFZ_GeoForschungsZentrum_Potsdam,_Helmholtz_Centre. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Ingo Sasgen, Bert Wouters, Alex S. Gardner, Michalea D. King, Marco
Tedesco, Felix W. Landerer, Christoph Dahle, Himanshu Save, Xavier
Fettweis. Return to rapid ice loss in Greenland and record loss in
2019 detected by the GRACE-FO satellites. Communications Earth &
Environment, 2020; 1 (1) DOI: 10.1038/s43247-020-0010-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200820143827.htm

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