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Greenland’s Contribution to Sea Level Rise Doubled During 2011-2014 — Larger Melt Pulses on the Horizon
18
July, 2016
According
to a new report, the
Greenland Ice Sheet lost one trillion tons of water due to melt
during the four-year period from 2011 through 2014. That’s about
double the typical rate of loss during the 1990s through mid-2000s.
Subsequently, Greenland’s contribution to sea-level rise also
doubled. As a result, Greenland alone contributed 0.75 mm of
sea-level rise every year during the 2011 to 2014 period.
(The
above video briefly explains the findings of a
new scientific study indicating
a doubling in the rate of Greenland melt during 2011 through 2014.)
Bear
in mind, the study focuses on Greenland only. Those numbers don’t
include thermal expansion from the world’s warming oceans. Nor do
they include an increasing amount of melt from Antarctica. Nor do
they include large volumes of melt coming from the world’s rapidly
disappearing mountain glaciers. Together, all of these in total are
pushing sea levels higher by around 4 mm per year during the 2011
through 2016 period. That’s about 1 mm more per year than the 1993
to 2009 period. But the greater additional contribution appears to be
coming from melting glaciers in Greenland and Antarctica.
The
new Greenland Study found
that melt averaged around 250 billion tons per year over the
four-year period. This included a single melt year, 2012, in which
Greenland contributed about half a trillion tons
of melt water. The massive 2012 melt was spurred by high Greenland
surface temperatures during summer which resulted in spiking surface
melt rates during June, July, and August. At the time, a powerful
high pressure system focused heat across the ice sheet which caused
most of the surface area of Greenland’s glaciers to experience
melt.
During 2011–2014, Greenland mass loss averaged 269 ± 51 Gt/yr. Atmospherically driven losses were widespread, with surface melt variability driving large fluctuations in the annual mass deficit. Terminus regions of five dynamically thinning glaciers, which constitute less than 1% of Greenland’s area, contributed more than 12% of the net ice loss. This high-resolution record demonstrates that mass deficits extending over small spatial and temporal scales have made a relatively large contribution to recent ice sheet imbalance.
In
other words, melt at the margins of the ice sheet and large surface
melt pulses during brief periods were the primary contributors to
increasing melt rated during the study period.
(Annual
mass losses from Greenland and Antarctica are accelerating. This
results in increasing rates of global sea level rise. While mass loss
in Antarctica has recently primarily been driven by basal melt,
surface melt has been the chief contributor to Greenland mass loss.
In addition, the highly variable nature of surface mass loss along
with its tendency to create brief, intense melt pulses is some cause
for concern. Image source: Charting
Ice Sheet Contributions to Global Sea Level Rise.)
The
study found that surface melt rates were highly variable and
dependent upon weather —with
a strongly negative North Atlantic Oscillation contributing to
conditions that enhanced melt during 2012.
In this case, it appears that natural variability is beginning to be
pushed by human-forced warming into a phase where certain years will
preferentially further enhance Greenland melt. To this point, the
tendency for large surface melt spikes was found to have increased
during recent years. In contrast to Antarctica, where warming oceans
contact glacial cliff faces and ice shelf undersides to accelerate
melt, in Greenland, surface melt appears to currently be playing a
bigger role in driving melt acceleration.
Surface
melt can produce odd and unstable patterns of melt ponding and runoff
over large ice sheets like Greenland. And as Greenland continues to
warm due to human-forced climate change, an
increasing risk of glacial outburst floods can be the result.
The highly variable nature of surface melt is also a concern. In
other words, overall warming can produce extreme, if brief, periods
of warmth over Greenland that produce disproportionately large melt
spikes. In this case, 2012 should not be seen as an outlier, but as
the first of many future strong surface melt years — ones that will
almost certainly surpass that year in melt intensity unless
human-forced warming is somehow brought to a halt.
Links/Attribution/Statements
Hat
tip to Colorado Bob
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