"Global Meltdown"

From the Guardian:

Scientists fear that global warming will bring climatic turbulence, with changes coming in big jumps rather than gradually...

The story of research into sea level rise is typical of how perceptions have changed in the past five years. The conventional view - you can still read it in reports from the UN's Intergovernmental Panel on Climate Change - holds that sea levels will start to rise as a pulse of warming works its way gradually from the surface through the 2km- and 3km-thick ice sheets on Greenland and Antarctica, melting them. The ice is thick and the heat will penetrate only slowly. So we have hundreds, probably thousands, of years to make our retreat to higher ground.

Recent research, however, shows that idea is wholly wrong. Glaciologists forgot about crevasses. What is actually happening is that ice is melting at the surface and forming lakes that drain down into the crevasses. In 10 seconds, the water is at the base of the ice sheet, where it lubricates the join between ice and rock. Then the whole ice sheet starts to float downhill towards the ocean.

"These flows completely change our understanding of the dynamics of ice sheet destruction," says Alley. "Even five years ago, we didn't know about this."

This summer, lakes several kilometres across formed on the Greenland ice sheet, and drained away to the depths. Scientists measured how, within hours of the lakes forming, the vast ice sheets physically rose up, as if floating on water, and slid towards the ocean. That is why Greenland glaciers are flowing faster, and there are more icebergs breaking off into the Atlantic Ocean. That is why average sea level rise has increased from 2mm a year in the early 1990s to more than 3mm a year now.

Soon it could be a great deal more. Jim Hansen of Nasa, George Bush's top climate modeller, predicts that sea level rise will be 10 times faster within a few years, as Greenland destabilises. "Building an ice sheet takes a long time," he says. "But destroying it can be explosively rapid."

Alarmist? No. It has happened before, he says. During the final few centuries of the last ice age, the sea level rose 20 metres in 400 years, an average of 20 times faster than now. These were sudden, violent times. And the melting was caused by tiny wobbles in the Earth's orbit that changed the heat balance of the planet by only a fraction as much as our emissions of greenhouse gases are doing today.

Violent change

There is more evidence of abrupt and violent change, most of it culled from ice cores, lake sediments, tree rings and other natural archives of climate. We now know that the last ice age was not a stable cold era but near-permanent climate change. Towards the end, around 11,000 years ago, average temperatures in parts of the Arctic rose by 16C or more within a decade. Alley believes it happened within a single year, though he says the evidence in the ice cores is not precise enough to prove it....