March 20, 2008
Arctic Ice Returns, Thin and Tentative
Arctic ice has
reformed rapidly this winter after a record summer low, but it still covers
less of the Arctic Ocean than it did in previous decades, NASA scientists
announced today in an update of the states of Arctic
and Antarctic sea ice.
the month where Arctic sea ice traditionally hits its highest extent after the
Northern Hemisphere winter and Antarctic sea ice reaches its lowest extent.
NASA satellites have monitored sea ice coverage over both poles for nearly 40
ice reached a record low
this past summer, with 23 percent less sea ice cover than the previous record
low and 39 percent less than the average amount that has previously spanned the
Arctic Ocean in the summer months.
extraordinarily high melt opened the fabled Northwest
Passage and spurred scientists' worries about whether the Arctic ice had
reached a tipping point, where melting begins to spiral out of control.
satellite observations showed that while this winter's ice extent didn't dip
below previous records, it was still well below the average amount seen in the
ice has largely remained stable over the years of NASA's observations. The
Antarctic has little long-term sea ice and a different climate and weather
regime than the Arctic.
The area of
ocean covered by sea ice isn't the only factor in the "health" of the
ice comes in two types: older, thicker perennial ice that has survived at least
one summer melt season and younger, thinner seasonal ice that forms in the
winter and melts again in the summer.
ice melts more easily because it is thin and salty, and so "it's flexible
and crushable and more susceptible to winds and currents," said Seelye
Martin of NASA's Cryospheric Sciences Program.
temperatures in parts of the Arctic increased
the amount of thin, seasonal ice that formed this winter. So while Arctic sea
ice was dominated by multiyear, perennial ice in past decades , it is mostly now
younger, newly-formed ice.
of older, perennial sea ice has substantially decreased over the past few
years, and "has reached an all-time minimum," Martin said. This low
is in part due to the substantial 2007 summer melt, attributed in part to climate
Future of the Arctic
colder temperatures and the slightly higher winter extent this year will mean
come summer is uncertain. But because the majority of the ice is young and
thin, it would be more susceptible to summer melt.
perennial sea ice will recover is also uncertain, but "it's not likely
that the perennial ice cover will recover [to where it was in the past] in the
near future," said Josefino Comiso of NASA's Goddard Space Flight Center
in Greenbelt, Md.
Some of the
seasonal ice could become perennial sea ice if summer conditions are cooler
than normal this year, Meier noted, as some of the seasonal ice has formed
higher north than ever before.
"one cold summer is not going to do it, one cold winter is not going to do
it," Meier said. Numerous years of colder temperatures would be needed to
restore the Arctic sea ice to where it was in the 1980s, and that is not likely
to happen with the increasing levels of heat-trapping greenhouse gases in the
atmosphere, he added.