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
Published: 17 February 2006
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.
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
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
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