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

A A A

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. None of the current climate and ice models predict this. But I prefer the evidence from the Earth's history and my own eyes. 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

Voices
voicesGood for Lana Del Rey for helping kill that myth, writes Grace Dent
News
The University of California study monitored the reaction of 36 dogs
sciencePets' range of emotions revealed
Life and Style
fashion Designs are part of feminist art project by a British student
Arts and Entertainment
The nomination of 'The Wake' by Paul Kingsnorth has caused a stir
books
PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
Arts and Entertainment
The Tour de France peloton rides over a bridge on the Grinton Moor, Yorkshire, earlier this month
film
News
Snoop Dogg pictured at The Hollywood Reporter Nominees' Night in February, 2013
people... says Snoop Dogg
News
i100
Life and Style
food + drinkZebra meat is exotic and lean - but does it taste good?
Arts and Entertainment
Residents of Derby Road in Southampton oppose filming of Channel 4 documentary Immigration Street in their community
tv
Voices
voicesSiobhan Norton on why she eventually changed her mind
News
i100
Extras
indybest
Sport
Scottish singer Susan Boyle will perform at the Commonwealth Games opening ceremony in Glasgow
commonwealth games
Arts and Entertainment
Dwayne 'The Rock' Johnson stars in Hercules
filmReview: The Rock is a muscular Davy Crockett in this preposterous film, says Geoffrey Macnab
Life and Style
tech
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
iJobs Job Widget
iJobs General

VB.Net Developer

£35000 - £45000 per annum + competitive: Progressive Recruitment: If you're pa...

SAP Business Consultant (SD, MM and FICO), £55,000, Wakefield

£45000 - £55000 per annum + competitive: Progressive Recruitment: SAP Business...

Java Developer

£40000 - £60000 per annum + competitive: Progressive Recruitment: My client, a...

SAP Functional Consultant (SD, MM and FICO), £45,000 - £55,000.

£45000 - £55000 per annum + Benefits: Progressive Recruitment: SAP Functional ...

Day In a Page

Noel Fielding's 'Luxury Comedy': A land of the outright bizarre

Noel Fielding's 'Luxury Comedy'

A land of the outright bizarre
What are the worst 'Word Crimes'?

What are the worst 'Word Crimes'?

‘Weird Al’ Yankovic's latest video is an ode to good grammar. But what do The Independent’s experts think he’s missed out?
Can Secret Cinema sell 80,000 'Back to the Future' tickets?

The worst kept secret in cinema

A cult movie event aims to immerse audiences of 80,000 in ‘Back to the Future’. But has it lost its magic?
Facebook: The new hatched, matched and dispatched

The new hatched, matched and dispatched

Family events used to be marked in the personal columns. But now Facebook has usurped the ‘Births, Deaths and Marriages’ announcements
Why do we have blood types?

Are you my type?

All of us have one but probably never wondered why. Yet even now, a century after blood types were discovered, it’s a matter of debate what they’re for
Honesty box hotels: You decide how much you pay

Honesty box hotels

Five hotels in Paris now allow guests to pay only what they think their stay was worth. It seems fraught with financial risk, but the honesty policy has its benefit
Commonwealth Games 2014: Why weight of pressure rests easy on Michael Jamieson’s shoulders

Michael Jamieson: Why weight of pressure rests easy on his shoulders

The Scottish swimmer is ready for ‘the biggest race of my life’ at the Commonwealth Games
Some are reformed drug addicts. Some are single mums. All are on benefits. But now these so-called 'scroungers’ are fighting back

The 'scroungers’ fight back

The welfare claimants battling to alter stereotypes
Amazing video shows Nasa 'flame extinguishment experiment' in action

Fireballs in space

Amazing video shows Nasa's 'flame extinguishment experiment' in action
A Bible for billionaires

A Bible for billionaires

Find out why America's richest men are reading John Brookes
Paranoid parenting is on the rise - and our children are suffering because of it

Paranoid parenting is on the rise

And our children are suffering because of it
For sale: Island where the Magna Carta was sealed

Magna Carta Island goes on sale

Yours for a cool £4m
Phone hacking scandal special report: The slide into crime at the 'News of the World'

The hacker's tale: the slide into crime at the 'News of the World'

Glenn Mulcaire was jailed for six months for intercepting phone messages. James Hanning tells his story in a new book. This is an extract
We flinch, but there are degrees of paedophilia

We flinch, but there are degrees of paedophilia

Child abusers are not all the same, yet the idea of treating them differently in relation to the severity of their crimes has somehow become controversial
The truth about conspiracy theories is that some require considering

The truth about conspiracy theories is that some require considering

For instance, did Isis kill the Israeli teenagers to trigger a war, asks Patrick Cockburn