 |
| Seasonal melting of arctic sea ice has set a record due to global warming |
By Justin Gillis, The New York Times, September 19, 2012
The drastic melting
of Arctic sea ice has finally ended for the year, scientists announced Wednesday, but not before
demolishing the previous record — and setting off new warnings about the rapid
pace of change in the region.
The apparent low point for 2012 was reached Sunday, according to the National Snow and Ice Data
Center, which said that sea ice that day covered about 1.32 million
square miles, or 24 percent, of the surface of the Arctic Ocean. The previous
low, set in 2007, was 29 percent.
When satellite tracking began in the late 1970s, sea ice at its lowest
point in the summer typically covered about half the Arctic Ocean, but it has
been declining in fits and starts over the decades.
“The Arctic is the earth’s air-conditioner,” said Walt
Meier, a research scientist at the snow and ice center, an agency
sponsored by the government. “We’re losing that. It’s not just that polar bears
might go extinct, or that native communities might have to adapt, which we’re
already seeing — there are larger climate effects.”
His agency waited a few days before announcing the low to be sure sea
ice had started to refreeze, as it usually does at this time of year, when
winter closes in rapidly in the high Arctic. A shell of ice will cover much of
the Arctic Ocean in coming months, but it is likely to be thin and prone to
melting when summer returns.
Scientists consider the rapid warming of the region to be a
consequence of the human release of greenhouse gases, and they see the melting
as an early warning of big changes to come in the rest of the world.
Some of them also think the collapse of Arctic sea ice has already
started to alter atmospheric patterns in the Northern
Hemisphere, contributing to greater extremes of weather in the United States
and other countries, but that case is not considered proven.
The sea ice is declining much faster than had been predicted in the
last big United Nations report on the state of the climate, published
in 2007. The most sophisticated computer analyses for that report suggested
that the ice would not disappear before the middle of this century, if then.
Now, some scientists think the Arctic Ocean could be largely free of
summer ice as soon as 2020. But governments have not responded to the change
with any greater urgency about limiting greenhouse emissions. To the contrary,
their main response has been to plan for exploitation of newly accessible
minerals in the Arctic, including drilling for more oil.
Scientists said Wednesday that the Arctic has become a prime example of
the built-in conservatism of their climate forecasts. As dire as their warnings about the long-term consequences of
heat-trapping emissions have been, many of them fear they may still be
underestimating the speed and severity of the impending changes.
In a panel discussion on Wednesday in New York sponsored by
Greenpeace, the environmental group, James E. Hansen, a prominent NASA climate
scientist, said the Arctic melting should serve as a warning to the public of
the risks that society is running by failing to limit emissions.
“The scientific community realizes that we have a planetary
emergency,” Dr. Hansen said. “It’s hard for the public to recognize this
because they stick their head out the window and don’t see that much going on.”
A prime concern is the potential for a large rise in the level of the
world’s oceans. The decline of Arctic sea ice does not contribute directly to
that problem, since the ice is already floating and therefore displacing its
weight in water.
But the disappearance of summer ice cover replaces a white, reflective
surface with a much darker ocean surface, allowing the region to trap more of
the sun’s heat, which in turn melts more ice. The extra heat in the ocean
appears to be contributing to an accelerating melt of the nearby Greenland ice
sheet, which does contribute to the rise in sea level.
At one point this summer, surface melt was occurring across 97 percent
of the Greenland ice sheet, a development not seen before in the era of
satellite measurements, although geological research suggests that it has
happened in the past.
The sea is now rising at a rate of about a foot per century, but
scientists like Dr. Hansen expect this rate to increase as the planet warms,
putting coastal settlements at risk.
A scientist at the snow and ice center, Julienne
C. Stroeve, hitched a ride on a Greenpeace ship in recent weeks to
inspect the Arctic Ocean for herself. Interviewed this week after putting into
port at the island of Spitsbergen, she said one of her goals had been to debark
on ice floes and measure them, but that it had been difficult to find any large
enough to support her weight.
Ice
floes were numerous in spots, she said, but “when we got further into the ice
pack, there were just large expanses of open water.
No comments:
Post a Comment