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Arctic sea ice reaches record low, Nasa says

2012-08-28 07:18:43

By Roger Harrabin Environment analyst

The Arctic has lost more sea ice this year than at any time since satellite

records began in 1979, Nasa says.

Scientists involved in the calculations say it is part of a fundamental change.

What is more, sea ice normally reaches its low point in September so it is

thought likely that this year's melt will continue to grow.

Nasa says the extent of sea ice was 1.58m sq miles (4.1m sq km) compared with a

previous low of 1.61m sq miles (4.17m sq km) on 18 September 2007.

The sea ice cap grows during the cold Arctic winters and shrinks when

temperatures climb again, but over the last three decades, satellites have

observed a 13% decline per decade in the summertime minimum.

The thickness of the sea ice is also declining, so overall the ice volume has

fallen far - although estimates vary about the actual figure.

Joey Comiso, senior research scientist at Nasa's Goddard Space Flight Center,

said this year's ice retreat was caused by previous warm years reducing the

amount of perennial ice - which is more resistant to melting. It's created a

self-reinforcing trend.

"Unlike 2007, temperatures were not unusually warm in the Arctic this summer.

[But] we are losing the thick component of the ice cover," he said. "And if you

lose [that], the ice in the summer becomes very vulnerable."

'Inevitable death'

Walt Meier, from the National Snow and Ice Data Center that collaborates in the

measurements, said: "In the context of what's happened in the last several

years and throughout the satellite record, it's an indication that the Arctic

sea ice cover is fundamentally changing."

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The summer ice volume is now only 30% of what it was in the 1980s

Prof Peter Wadhams Cambridge University

Professor Peter Wadhams, from Cambridge University, told BBC News: "A number of

scientists who have actually been working with sea ice measurement had

predicted some years ago that the retreat would accelerate and that the summer

Arctic would become ice-free by 2015 or 2016.

"I was one of those scientists - and of course bore my share of ridicule for

daring to make such an alarmist prediction."

But Prof Wadhams said the prediction was now coming true, and the ice had

become so thin that it would inevitably disappear.

"Measurements from submarines have shown that it has lost at least 40% of its

thickness since the 1980s, and if you consider the shrinkage as well it means

that the summer ice volume is now only 30% of what it was in the 1980s," he

added.

"This means an inevitable death for the ice cover, because the summer retreat

is now accelerated by the fact that the huge areas of open water already

generated allow storms to generate big waves which break up the remaining ice

and accelerate its melt.

Infographic

"Implications are serious: the increased open water lowers the average albedo

[reflectivity] of the planet, accelerating global warming; and we are also

finding the open water causing seabed permafrost to melt, releasing large

amounts of methane, a powerful greenhouse gas, to the atmosphere."

Threats and opportunities

Opinions vary on the date of the demise of summer sea ice, but the latest

announcement will give support to those who err on the pessimistic side.

Greenpeace activist boards oil rig, 24 August 2012 Greenpeace is strongly

opposing attempts to exploit the Arctic

A recent paper from Reading University used statistical techniques and

computers to estimate that between 5-30% of the recent ice loss was due to

Atlantic Multi-decadal Oscillation - a natural climate cycle repeating every

65-80 years. It's been in warm phase since the mid 1970s.

But the rest of the warming, the paper estimates, is caused by human activity -

pollution and clearing of forests.

If the ice continues to disappear in summer there will be opportunities as well

as threats.

Some ships are already saving time by sailing a previously impassable route

north of Russia.

Oil, gas and mining firms are jostling to exploit the Arctic - although they're

being strongly opposed by environmentalists. Greenpeace has been protesting at

drilling by the Russian giant Gazprom.

Among the many threats, the warming is bad for Arctic wildlife. Thanks to the

influence of sea ice on the jet stream the changes could affect weather in the

UK.

The changes - if they happen - could unlock frozen deposits of methane which

would further overheat the planet.

Warmer seas could lead to more melting of Greenland's ice cap which would

contribute to raising sea levels and changing the salinity of the sea, which in

turn could alter ocean currents that help govern our climate.