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The jet fuel you burned on that flight from New York City to London? Say goodbye to 1 square meter of Arctic sea ice. Since at least the 1960s, the shrink- age of the ice cap over the Arctic
Ocean has advanced in lockstep with the
amount of greenhouse gases humans have
sent into the atmosphere, according to a
study published this week in Science. Ev-
ery additional metric ton of carbon dioxide
(CO2) puffed into the atmosphere appears to
cost the Arctic another 3 square meters of
summer sea ice—a simple and direct obser-
vational link that has been sitting in data
beneath scientists’ noses. “It’s really basic,”
says co-author Dirk Notz, a sea ice
expert at the Max Planck Institute
for Meteorology in Hamburg, Ger-
many. “In retrospect, it sounds like
something someone should have
done 20 years ago.”
If both the linear relationship
and current emission trends hold
into the future, the study sug-
gests the Arctic will be ice free by
2045—far sooner than some cli-
mate models predict. The study
suggests that those models are un-
derestimating how warm the Arc-
tic has already become and how
fast that melting will proceed. And
it gives the public and policymak-
ers a concrete illustration of the
consequences of burning fossil fuels, says
Edward Maibach, director of the Center for
Climate Change Communication at George
Mason University in Fairfax, Virginia. “Con-
crete information is always more engaging
than abstract information,” he says.
According to the new calculations, for
instance, the average annual carbon emis-
sions from a U.S. family of four would claim
nearly 200 square meters of sea ice. Over
3 decades, that family would be responsible
for destroying more than an American foot-
ball field’s worth of ice—a tangible threat
to ice-dependent creatures such as polar
bears. The study also makes for vivid com-
parisons between nations: Each person in
the United States, for instance, is responsi-
ble for the destruction of 10 times as much
ice each year as someone in India (see
graphic, below).
Sea ice retreat is already a poster child
for global warming, and some earlier studies had shown that the retreat closely tracks
atmospheric CO2 levels. But Notz and co-author Julienne Stroeve, an expert in sea
ice satellite measurements at the National
Snow and Ice Data Center in Boulder, Colorado, identified a tighter link to human activity by compiling annual human-caused
greenhouse gas emissions and comparing
those numbers with historic observations of
Arctic sea ice coverage during September—
when sea ice is at its smallest. To avoid
problems with year-to-year ice fluctuations,
they used a 30-year moving average of ice
coverage, allowing them to study the years
from 1968 to 2000.
To see whether the linear
relationship they found between emissions and sea ice also
emerged in computer simulations,
they checked 36 of the world’s major climate models. In simulations
in which CO2 levels rose 1% every
year, they found the same telltale
pattern every time, Stroeve says.
Yet the models’ sensitivity was off:
They tended to underestimate the
amount of ice loss. “Models are
not perfect,” Stroeve says. “And if
you can use observations by themselves to forecast when Arctic ice
will go away maybe that’s in some
ways better.”
IN DEPTH
By Warren Cornwall
CLIMATE CHANGE
Sea ice shrinks in step with carbon emissions
Models may underestimate the pace of ice loss because they are missing Arctic warming
One metric ton of
CO2 costs the Arctic
3 square meters of
summer sea ice.
0 15 30 45 60
Sea ice melted
per person per
year (m2)
4 NOVEMBER 2016 • VOL 354 ISSUE 6312 533
On thin ice
Based on CO2 emissions in 2013, each U.S. resident led to the melting of 49
square meters of Arctic sea ice—nearly 10 times as much as someone in India.
