Climate Change: On the Edge
Shadow of Extinction
February 25, 2006
Climate Change: On the Edge
by Jim Hansen
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| NASA top climate scientist, James Hansen |
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 behavior of the ice streams that are draining the Greenland ice sheet. They show that Greenland seems to be losing at least 200 cubic kilometers 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 kilometers 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 meters 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 stabilize 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 modeler. This article was originally published in The Independent of London on February 18, 2006.
On February 4, 2006, NASA's Chief Climate Scientist, James Hansen joined Eco-Talk's Betsy Rosenberg on Air America Radio to discuss Global Warming and the Bush administration's efforts to rewrite the facts. You can listen in to the audio interview: http://www.airamericaradio.com/onnow/clips/clip/2628
Shadow of Extinction
George Monbiot / The Guardian
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| The planet has experienced massive die-offs in the past but this time we seem to be headed towards a man-made catastrophe. Credit: Friends of the Earth/ Europe |
LONDON -- It is old news, I admit. Two hundred and fifty-one million years old, to be precise. But the story of what happened then, which has now been told for the first time, demands our urgent attention. Its implications are more profound than anything taking place in Iraq, or Washington, or even (and I am sorry to burst your bubble) Wimbledon. Unless we understand what happened, and act upon that intelligence, prehistory may very soon repeat itself, not as tragedy, but as catastrophe.
The events that brought the Permian period (between 286 million and 251 million years ago) to an end could not be clearly determined until the mapping of the key geological sequences had been completed. Until recently, paleontologists had assumed that the changes that took place then were gradual and piecemeal. But three years ago a precise date for the end of the period was established, which enabled geologists to draw direct comparisons between the rocks laid down at that time in different parts of the world.
Having done so, they made a shattering discovery. In China, South Africa, Australia, Greenland, Russia and Svalbard, the rocks record an almost identical sequence of events, taking place not gradually, but relatively instantaneously. They show that a cataclysm caused by natural processes almost brought life on Earth to an end. They also suggest that a set of human activities that threatens to replicate those processes could exert the same effect, within the lifetimes of some of those who are on earth today.
As the professor of paleontology Michael Benton records in his new book, When Life Nearly Died, the marine sediments deposited at the end of the Permian period record two sudden changes. The first is that the red, green, or gray rock laid down in the presence of oxygen is suddenly replaced by black muds of the kind deposited when oxygen is absent. At the same time, an instant shift in the ratio of the isotopes alternative forms) of carbon within the rocks suggests a spectacular change in the concentration of atmospheric gases. On land, another dramatic transition has been dated to precisely the same time. In Russia and South Africa, gently deposited mudstones and limestones suddenly give way to massive dumps of pebbles and boulders.
But the geological changes are minor in comparison with what happened to the animals and plants. The Permian was one of the most biologically diverse periods in the earth's history. Herbivorous reptiles the size of rhinos were hunted through forests of tree ferns and flowering trees by saber-toothed predators. At sea, massive coral reefs accumulated, among which lived great sharks, fish of all kinds and hundreds of species of shell creatures.
Then suddenly there is almost nothing. The fossil record very nearly stops dead. The reefs die instantly, and do not reappear on earth for 10 million years. All the large and medium-sized sharks disappear, most of the shell species, and even the great majority of the toughest and most numerous organisms in the sea, the plankton. Among many classes of marine animals, the only survivors were those adapted to the near-absence of oxygen.
On land, the shift was even more severe. Plant life was almost eliminated from the earth's surface. The four-footed animals, the category to which humans belong, were nearly exterminated: so far only two fossil reptile species have been found anywhere on earth that survived the end of the Permian. The world's surface came to be dominated by just one of these, an animal a bit like a pig. It became ubiquitous because nothing else was left to compete with it or to prey upon it.
Altogether, Benton shows, some 90% of the Earth's species appear to have been wiped out: this represents by far the gravest of the mass extinctions. The world's "productivity" (the total mass of biological matter) collapsed.
Ecosystems recovered very slowly. No coral reefs have been found anywhere on earth in the rocks laid down over the following 10 million years. One 150 million years elapsed before the world once again became as bio-diverse as in the Permian.
So what happened? Some scientists have argued that the mass extinction was caused by a meteorite. But the evidence they put forward has been undermined by further studies. There is a more persuasive case for a different explanation. For many years, geologists have been aware that at some point during or after the Permian there was a series of gigantic volcanic eruptions in Siberia. The lava was dated properly for the first time in the early 1990s.
We now know that the principal explosions took place 251 million years ago, precisely at the point at which life was almost extinguished. The volcanoes produced two gases: sulfur dioxide and carbon dioxide. The sulfur and other effusions caused acid rain, but would have bled from the atmosphere quite quickly. The carbon dioxide, on the other hand, would have persisted. By enhancing the greenhouse effect, it appears to have warmed the world sufficiently to have destabilized the super concentrated frozen gas called methane hydrate, locked in sediments around the polar seas. The release of methane into the atmosphere explains the sudden shift in carbon isotopes.
Methane is an even more powerful greenhouse gas than carbon dioxide. The result of its release was runaway global warming: a rise in temperature led to changes that raised the temperature further, and so on. The warming appears, alongside the acid rain, to have killed the plants. Starvation then killed the animals.
Global warming also seems to explain the geological changes. If the temperature of the surface waters near the poles increases, the circulation of marine currents slows down, which means that the ocean floor is deprived of oxygen. As the plants on land died, their roots would cease to hold together the soil and loose rock, with the result that erosion rates would have greatly increased.
So how much warming took place? A sharp change in the ratio of the isotopes of oxygen permits us to reply with some precision: 6C. Benton does not make the obvious point, but another author, the climate change specialist Mark Lynas, does. Six degrees is the upper estimate produced by the UN's scientific body, the intergovernmental panel on climate change (IPCC), for global warming by 2100. A conference of some of the world's leading atmospheric scientists in Berlin last month concluded that the IPCC's model may have underestimated the problem: the upper limit, they now suggest, should range between 7 and 10 degrees. Neither model takes into account the possibility of a partial melting of the methane hydrate still present in vast quantities around the fringes of the polar seas.
Suddenly, the events of a quarter of a billion years ago begin to look very topical indeed. One of the possible endings of the human story has already been told. Our principal political effort must now be to ensure that it does not become set in stone.
George Monbiot's book The Age of Consent: a Manifesto for a New World Order is published by Flamingo. His website is www.monbiot.com.
This essay previously appeared in the Guardian of London (© Guardian Newspapers) and on Common Dreams Web site (commondreams.org/views03/0701-06.htm)
(Reposted in accordance with Title 17 US Code, Section 10, for research and educational purposes.)
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