Wednesday, September 28, 2005

Arctic ice 'disappearing fast'

http://news.bbc.co.uk/1/hi/sci/tech/4290340.stm

Reported by the BBC :

New data from US scientists shows that the area covered by sea ice in the Arctic has shrunk for a fourth consecutive year.

They say that September 2005 sees the lowest extent of ice cover for more than a century.

The researchers conclude that human-induced global warming is at least partially responsible...

The Arctic Climate Impact Assessment, a four-year study involving hundreds of scientists, projected an additional temperature rise of 4-7C by 2100.

If the current trend can be ascribed in part to human-induced climate change, Mark Serreze sees major reasons for concern.

'What we're seeing is a process in which we start to lose ice cover during the summer,' he said, 'so areas which formerly had ice are now open water, which is dark.

'These dark areas absorb a lot of the Sun's energy, much more than the ice; and what happens then is that the oceans start to warm up, and it becomes very difficult for ice to form during the following autumn and winter.

'It looks like this is exactly what we're seeing - a positive feedback effect, a 'tipping-point'.'

The idea behind tipping-points is that at some stage the rate of global warming would accelerate, as rising temperatures break down natural restraints or trigger environmental changes which release further amounts of greenhouse gases.

Possible tipping-points include:

The disappearance of sea ice leading to greater absorption of solar radiation.

A switch from forests being net absorbers of carbon dioxide to net producers.

Melting permafrost, releasing trapped methane.



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