Sea ice in the Arctic’s coastal areas may be thinning twice as fast as earlier thought, a new modelling study led by UCL researchers reports...
Sea ice in the Arctic’s coastal areas may be thinning twice as fast as earlier thought, a new modelling study led by UCL researchers reports.
Sea ice thickness is determined by measuring the
height of the ice above water, and this measurement is distorted by snow
weighing the ice flow down.
In the new study, published in The Cryosphere, researchers
used the results of a new computer model designed to estimate snow depth as it
varies from year to year, concluding that sea ice in key coastal areas was
thinning at a rate that was 70 to 100 per cent faster than previously thought.
Robbie Mallett of UCL Earth Sciences, the PhD
student who led the study, said: “The thickness of sea ice is a sensitive
indicator of the health of the Arctic. It is important as thicker ice acts as
an insulating blanket, stopping the ocean from warming up the atmosphere in
winter, and protecting the ocean from the sunshine in summer. Thinner ice is
also less likely to survive during the Arctic summer melt.”
“Previous calculations of sea ice thickness are
based on a snow map last updated 20 years ago. Because sea ice has begun
forming later and later in the year, the snow on top has less time to
accumulate. Our calculations account for this declining snow depth for the
first time, and suggest the sea ice is thinning faster than we thought.”
Co-author Professor Julienne Stroeve, UCL Earth
Sciences, said: “There are a number of uncertainties in measuring sea ice
thickness but we believe our new calculations are a major step forward in terms
of more accurately interpreting the data we have from satellites.
“We hope this work can be used to better assess the
performance of climate models that forecast the effects of long-term climate
change in the Arctic — a region that is warming at three times the global rate,
and whose millions of sq km of ice are essential for keeping the planet cool.”
To calculate sea ice thickness researchers used
radar from the European Space Agency’s CryoSat-2 satellite. By timing how long
it takes for radar waves to bounce back from the ice, they can calculate the
height of the ice above the water, from which they can infer the ice’s total
thickness.
In the new study, researchers used a novel snow
model previously developed by researchers at UCL and Colorado State University,
SnowModel-LG, which calculates snow depth and density using inputs such as air
temperature, snowfall and ice motion data to track how much snow accumulates on
sea ice as it moves around the Arctic Ocean.
By combining the results of the snow model with
satellite radar observations, they estimated the overall rate of decline of sea
ice thickness in the Arctic, as well as the variability of sea ice thickness
from year to year.
They found that the rate of decline in the three
coastal seas of Laptev, Kara and Chukchi seas increased by 70, 98 and 110 per
cent respectively, when compared to earlier calculations. They also found that,
across all seven coastal seas, the variability in sea ice thickness from year
to year increased by 58 per cent.
Sea ice in the coastal seas varies from half a
metre to two metres in thickness. The ice in this region is not surviving the
summer melt. The faster thinning of sea ice in the coastal Arctic seas has
implications for human activity in the region, both in terms of shipping along
the Northern Sea Route for a larger part of the year, as well as the extraction
of resources from the sea floor such as oil, gas and minerals.
Mallett said: “More ships following the route
around Siberia would reduce the fuel and carbon emissions necessary to move
goods around the world, particularly between China and Europe.
“However, it also raises the risk of fuel spillages
in the Arctic, the consequences of which could be dire. The thinning of coastal
sea ice is also worrying for indigenous communities, as it leaves settlements
on the coast increasingly exposed to strong weather and wave action from the
emerging ocean.”
Mallett, Professor Stroeve and co-author Michel
Tsamados, UCL Earth Sciences, spent several weeks investigating snow and ice in
the Arctic onboard the German research vessel Polarstern, which explored the
central Arctic Ocean in 2019 and 2020.
The study was funded by the UK’s Natural
Environment Research Council, the European Space Agency, and the US National
Aeronautics and Space Administration.
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