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Climate Change: On the Edge

 

Greenland ice cap breaking up at twice the rate it was five years ago, says

scientist Bush tried to gag

 

By Jim Hansen

 

The Independent (UK) Published: 17 February 2006

 

http://news.independent.co.uk/environment/article345926.ece

 

 

 

A satellite study of the Greenland ice cap shows that it is melting far faster

than scientists had feared - twice as much ice is going into the sea as it was

five years ago. The implications for rising sea levels - and climate change -

could be dramatic.

 

Yet, a few weeks ago, when I - a Nasa climate scientist - tried to talk to the

media about these issues following a lecture I had given calling for prompt

reductions in the emission of greenhouse gases, the Nasa public affairs team -

staffed by political appointees from the Bush administration - tried to stop me

doing so. I was not happy with that, and I ignored the restrictions. The first

line of Nasa's mission is to understand and protect the planet.

 

This new satellite data is a remarkable advance. We are seeing for the first

time the detailed behaviour of the ice streams that are draining the Greenland

ice sheet. They show that Greenland seems to be losing at least 200 cubic

kilometres of ice a year. It is different from even two years ago, when people

still said the ice sheet was in balance.

 

Hundreds of cubic kilometres sounds like a lot of ice. But this is just the

beginning. Once a sheet starts to disintegrate, it can reach a tipping point

beyond which break-up is explosively rapid. The issue is how close we are

getting to that tipping point. The summer of 2005 broke all records for melting

in Greenland. So we may be on the edge.

 

Our understanding of what is going on is very new. Today's forecasts of

sea-level rise use climate models of the ice sheets that say they can only

disintegrate over a thousand years or more. But we can now see that the models

are almost worthless. They treat the ice sheets like a single block of ice that

will slowly melt. But what is happening is much more dynamic.

 

Once the ice starts to melt at the surface, it forms lakes that empty down

crevasses to the bottom of the ice. You get rivers of water underneath the ice.

And the ice slides towards the ocean.

 

Our Nasa scientists have measured this in Greenland. And once these ice streams

start moving, their influence stretches right to the interior of the ice sheet.

Building an ice sheet takes a long time, because it is limited by snowfall. But

destroying it can be explosively rapid.

 

How fast can this go? Right now, I think our best measure is what happened in

the past. We know that, for instance, 14,000 years ago sea levels rose by 20m in

400 years - that is five metres in a century. This was towards the end of the

last ice age, so there was more ice around. But, on the other hand, temperatures

were not warming as fast as today.

 

How far can it go? The last time the world was three degrees warmer than today -

which is what we expect later this century - sea levels were 25m higher. So that

is what we can look forward to if we don't act soon. I think sea-level rise is

going to be the big issue soon, more even than warming itself.

 

It's hard to say what the world will be like if this happens. It would be

another planet. You could imagine great armadas of icebergs breaking off

Greenland and melting as they float south. And, of course, huge areas being

flooded.

 

How long have we got? We have to stabilise emissions of carbon dioxide within a

decade, or temperatures will warm by more than one degree. That will be warmer

than it has been for half a million years, and many things could become

unstoppable. If we are to stop that, we cannot wait for new technologies like

capturing emissions from burning coal. We have to act with what we have. This

decade, that means focusing on energy efficiency and renewable sources of energy

that do not burn carbon. We don't have much time left.

 

Jim Hansen, the director of the Nasa Goddard Institute for Space Studies in New

York, is President George Bush's top climate modeller. He was speaking to Fred

Pearce (New Scientist)

 

 

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