The
Melting Arctic Is Covering Itself in a Warm Layer of Clouds
The
Arctic is melting. The first ice-free summer is coming. The whole
melting process is speeding up the warming of the entire Earth. And
every autumn, a layer of extra clouds are forming over the
ice-thinning Arctic that — researchers now believe — are speeding
that melting up.
In
a talk here March 4 at the March meeting of the American Physical
Society, Ariel Morrison, an atmospheric scientist at the University
of Colorado, Boulder, presented research that for the first time
offered a clear answer as to how the melting Arctic is changing its
clouds, and how those clouds in turn are changing the Arctic.
"Right
now, there's about a 20-year estimate: Between the 2040s and the
2060s, we're expecting to see the first ice-free summer,"
Morrison told Live Science. "This moves that toward the earlier
end of the estimates."
Modeling
how clouds impact the Arctic is complicated because they have two
different effects: They reflect light back into space before it can
hit the ground, and they act like a blanket that traps heat from
escaping from the planet's surface into space. The first effect cools
the ground, and the second warms it up.
When
the sun is out, every cloud does dual duty: reflecting incoming light
back into space, and reflecting radiating heat back toward the
ground. So it can be difficult to know whether, in any given
situation, clouds are doing more to warm the surface or keep it cool.
Until
Morrison's research, scientists weren't sure if the changing cloud
situation in the Arctic was speeding or slowing melting overall.
There were just too many factors involved.
Clouds
are also famously difficult to study in climate science in general.
And in the Arctic, matters are further complicated by the vast,
ice-free North Atlantic Ocean that has lots of cloud cover in the sky
but no sea ice due to the warm underwater currents that keep the
ocean's surface above the freezing point. Morrison developed a "mask"
that cut out all the noisy, unnecessary extra data from the North
Atlantic so she could target regions where the clouds were actually
relevant to melting.
Once
she narrowed down the model to target the clouds she was focused on,
Morrison found that the melting Arctic isn't dramatically changing
the reflective, cooling effect of clouds. In the summer, most clouds
in the Arctic form from moisture that flows through the atmosphere
from warmer southern latitudes. So the yearly increase in open water
in the Arctic doesn't have a big effect on total cloudiness during
the months when clouds are most crucial to reflecting light back into
space.
"If
we had found that summer clouds were responding to sea-ice loss —
so you melt some ice, a cloud forms on top of it — then clouds
would have this negative feedback with sea ice," she said.
In
other words, as sea ice melted, clouds would do more to cool the
Arctic.
But
it turns out, the summer melt has no significant impact on clouds.
However,
Morrison found, things are different in the fall. During those
months, it turns out, the skies above patches of open water are much
more likely to be cloudy. And those clouds do much more to trap heat
than to reflect light into space.
"It's
very, very seasonal in the Arctic," Morrison said. "Because
the Arctic only has sunlight for about six months out of the year,
and it's strongest in the middle of the summer. So only in the middle
of the summer, only in the middle of July, do clouds have this
cooling effect, because they're reflecting away more [light] than
they're [trapping]."
The
rest of the year, more clouds means more heat. And during the fall,
less ice also seems to mean more clouds. So as the Arctic melts, it's
effectively covering itself in a seasonal blanket that makes that
melting happen even faster.
Morrison
said she hopes her research will, in the future, factor in to Arctic
climate models, so they can more precisely plot out the future of the
quickly warming region. Her research has yet to be published in a
peer-reviewed scientific journal.
The
retreat of Arctic glaciers is exposing landscapes that haven't seen
the sun for nearly 120,000 years.
These
rocky vistas have very likely been covered in ice since the Eemian, a
period in which average temperatures were up to 3.6 degrees
Fahrenheit (2 degrees Celsius) warmer than present, and sea levels up
to 30 feet (9 meters) higher.
The Melting Arctic Is Covering Itself in a Warm Layer of Clouds
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