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, told Reuters.
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 sq km.
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
"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 in Oslo.
"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 or shipping.
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 faster.
"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. estimates.
Pachauri's authoritative 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," it adds.