Thaw May Be At ‘Tipping Point’
By Alister Doyle
OSLO - A
record melt of Arctic summer sea ice this month may be a sign that global
warming is reaching a critical trigger point that could accelerate the
northern thaw, some scientists say.
“The reason so much
(of the Arctic ice) went suddenly is that it is hitting a tipping point
that we have been warning about for the past few years,” James
Hansen, director of NASA’s Goddard Institute for Space Studies,
The Arctic summer sea ice
shrank by more than 20 percent below the previous 2005 record low in
mid-September to 4.13 million sq km (1.6 million sq miles), according
to a 30-year satellite record. It has now frozen out to 4.2 million
The idea of climate tipping
points — like a see-saw that suddenly flips over when enough weight
gets onto one side — is controversial because it is little understood
and dismissed by some as scaremongering about runaway effects.
The polar thaw may herald
a self-sustaining acceleration that could threaten indigenous peoples
and creatures such as polar bears — as Arctic sea ice shrinks,
the darker ocean soaks up ever more heat than reflective snow and ice.
In Germany, the Potsdam Institute
for Climate Impact Research says Arctic sea ice has “already tipped.”
Among potential “tipping
elements” that are still stable, it lists on its Web site a melt
of Siberian permafrost, a slowdown of the Gulf Stream and disruptions
to the Indian monsoon.
“I’d say we are
reaching a tipping point or are past it for the ice. This is a strong
indication that there is an amplifying mechanism here,” said Paal
Prestrud of the Center for International Climate and Environmental Research
“But that’s more
or less speculation. There isn’t scientific documentation other
than the observations,” he said.
SHIPPING, POLAR BEARS
Many experts now reckon Arctic
ice may disappear in summer before mid-century, decades before earlier
forecasts. The thaw would open the region to oil and gas exploration
Reuters will host a summit
of leading newsmakers on Oct 1-3 to review the state of the environment.
Speakers will include Rajendra Pachauri, the head of the U.N. Climate
Panel and Michael Morris, chief executive of American Electric Power.
“All models seem to
underestimate the speed at which the ice is melting,” said Anders
Levermann, a Potsdam professor.
“I do not believe that
this is alarmist… not all tipping points are irreversible,”
he said. And societies can weigh up remote risks, such as planes crashing
or nuclear meltdowns.
Hansen said he is seeking
more study of causes of the melt, widely blamed on greenhouse gases
from burning fossil fuels but perhaps slightly stoked by soot from forest
fires or industries in Russia and China. Ice darkened by soot melts
“It is a very good
lesson, because the ice sheets (on Greenland and Antarctica) have their
own tipping points, somewhat harder to get started but far more dangerous
for humanity around the globe,” he said.
A melt of floating Arctic
sea ice does not affect sea levels but Greenland has enough ice to raise
oceans by 7 meters and Antarctica by about 57 meters, according to U.N.
climate panel, in a summary report due for release in November, does
not use the phrase “tipping point” but does say: “Climate
change could lead to abrupt or irreversible climate changes and impacts.”
It says, for instance, that
it is “very unlikely” that the Gulf Stream bringing warm
water north to Europe will switch off this century. That could bring
a big regional cooling.
And it says that a melt of
ice sheets could lead to big sea level rises over thousands of years.
“Rapid sea level rise on century time scales cannot be excluded,”
© 2007 Reuters
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