The world of science was astounded when a record amount of
ice had melted on the Arctic Ocean by September 2007. But
even more ice melted away this year, and by September 16 only
1.4 million square miles of ice cover remained on the Arctic
Ocean. That is 49% less than the long-term average for September
in the years 1979–2000 (the first twenty years of satellite
observation).
The
coastlines of Siberia and Russia, Scandinavia, Alaska, and
most of Canada became ice-free by the end of last summer (first
figure at left). Compare this summer’s ice cover
(white) with the average location of the ice edge from 1979
to 2000 (purple curve), to appreciate the magnitude of the
change. Monitoring of ice cover in the Arctic
and Antarctic is done by the National
Snow and Ice Data Center.
The
volume of Arctic ice has declined faster than its area has,
as the thick, multi-year ice rapidly disappears. On the next
figure (below, left), the amount of ice is depicted by
age class from 1 to 5+ years. The older and thicker ice enables
part of the ice pack to survive the summertime melting season.
The ice that is 5 or more years old has now largely disappeared.
Compared to1983, there is practically no “old ice”
left. When spring arrives, more of the Arctic ice pack is
thinner than before, and is more prone to melt in the summer.
The
University of Washington estimates that the volume of sea
ice has reached an all-time low. Even after more new ice is
added in the upcoming winter, they estimate that in 2013 there
will only be 20% of the amount of five-year-old ice that was
present in 1983.
South of the Equator . . .
Only ten days after
the record low ice cover was observed in the Arctic, an all-time
high ice pack was seen in the Southern Ocean. Of course, it’s
winter in the South Polar region when it is summer in the
far North. The Southern Ocean pack ice surrounding Antarctica
has been expanding for years, not so much because the temperature
is shifting but because ever-faster winds in the southern
hemisphere caused the pack ice to expand northward. Loss of
ozone in the stratosphere over Antarctica (the famous "ozone hole") is believed to have
caused a stronger jet-stream, which ultimately ramped up
wind speeds in the lower atmosphere in that region.
Let’s
compare the changes in ice cover at the two poles. While the
Southern Ocean ice cover has grown, the increase has been
+6200 square miles per year over the last 32 years, an addition
somewhat larger than the state of Connecticut each year. Meanwhile,
the Arctic lost 35,500 square miles of ice each year, about
the size of the state of Indiana. And the loss has been much
faster since the year 2000.
Snow cover in the North has dwindled
even faster than sea ice
While disappearing
sea ice has been in the spotlight since 2007, snow cover has
been declining in the spring even more rapidly than the summertime
ice has in northern latitudes. According to a
new report2 by Chris Derksen and Ross Brown,
record low snow cover has been observed each spring in the
Eurasian Arctic for every successive year since 2008, and
in four of the last five years in Arctic Canada and Alaska.
The loss of snow in May and June is statistically significant.
The decline of June snow cover since 1979 (–21.5% per
decade) is twice the rate of loss of Arctic sea ice in September
(–11% per decade). Most climate models have not successfully
reproduced nor predicted the accelerating snowmelt in the
springtime, just as they have not reproduced the recent melting
of Arctic sea ice.
The consequences are not hard to imagine. Wherever and whenever
ice or snow covers the surface, they refrigerate the neighborhood
where they exist, and effectively counteract global warming
by reflecting 80 to 90% of the incoming solar energy back
to space. So most of the incoming energy is then lost forever.
With less snow on the land in May and June, and less ice covering
Arctic waters in late summer, the season when the surface
is dark becomes longer than before. Dark surfaces warm up
when they absorb sunlight and pass this warmth to the air
above. Voila! More global warming ensues in a previously
cold region, over a longer summer season. The warming observed
in the Arctic has been greater than what was predicted by
a variety of global climate models. The consequences of these
polar climatic changes are more far-reaching than one might
think at first.
_____________
CITATIONS
1. “Poles
apart: A record-breaking summer and winter” at National
Snow and Ice Data Center, Boulder, Colorado: http://nsidc.org/arcticseaicenews/2012/10/poles-apart-a-record-breaking-summer-and-winter/
.
2. “Spring
snow cover extent reductions in the 2008-2012 period exceeding
climate model projections” by Chris Derksen and
Ross Brown (2012), Geophysical Research Letters, vol.
39, 19, 10 oct. 2012, doi:10.1029/2012GL053387.
