Thanks to satellite data, scientists have finally figured out why Greenland's ice sheet is melting
Greenland’s
vast ice sheet continues to melt, and thanks to two recently-launched
satellites we’re beginning to understand why it’s happening so quickly.
Researchers at the University of Wisconsin-Madison believe increased
cloud cover over the ice sheet itself may be to blame for up to a third
of the ice melt that is occurring, a new study indicates. Clouds are
like nature’s blanket, and their effect on temperature is one of the
first things you learn in introductory meteorology courses. For an
example, think of temperatures at night when skies are clear versus when
it’s cloudy. On that clear night, the temperature falls quicker than on
a night where skies are overcast. Clouds, by nature, trap heat in the
atmosphere below them, causing temperatures to stay higher.
Professor Tristan L’Ecuyer says that his study found surface
temperatures were up to three degrees higher as a result of increased
cloud cover over the Greenland Ice Sheet. It does seem like the melt
itself may be causing a feedback loop of its own: moisture in the air is
a key component for cloud formation, which in turn traps heat in, which
causes more melting, which puts more moisture in the air and allows
more clouds to form.
Related: Oregon State University wants to use your computer to solve
climate issues How did L’Ecuyer and his team come to their conclusions?
It’s thanks to two new high tech NASA satellites launched over the past
decade, CloudSat and CALIPSO. The researchers took X-ray images of
clouds between 2007 and 2010 over the ice sheet to study cloud
composition and structure. From there, a team at the University of
Leuven in Belgium led by graduate student Kristof Van Tricht combined
the satellite data with ground observations and climate and snow model
simulations to understand the effects of these clouds on ice melt. “Once
you know what the clouds look like, you know how much sunlight they’re
going to reflect and how much heat from Earth’s surface they’re going to
keep in,” L’Ecuyer explains. What they found is that the normal daytime
ice melt was not refreezing at night, and was running off instead. That
process also fed on itself, accelerating the ice melt overall. This may
start to explain Greenland’s rapid ice loss in a more tangible form.
L’Ecuyer and Van Tricht’s work is important. One issue with present-day
climate models is their inability to properly resolve cloud cover. Most
models have far underestimated the amount of ice-sheet loss, in
something meteorologists and climatologists studying climate change
attribute to “cloud-climate feedback.” Resolve that issue, and climate
models may become a lot more accurate in the future. “This is something
we have to get right if we want to predict the future,” L’Ecuyer argues.
For those interested, the full study is available free of charge from
the Nature Communications website.
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