Scientists warn on climate tipping points

Alok Jha
The Guardian
Thursday August 16 2007

Some tipping points for climate change could be closer than previously thought. Scientists are predicting that the loss of the massive Greenland ice sheet may now be unstoppable and lead to catastrophic sea-level rises around the world.
In drawing together research on tipping points, where damage due to climate change occurs irreversibly and at an increasing rate, the researchers concluded that the risks were much greater than those predicted by the latest report by the Intergovernmental Panel on Climate Change (IPCC).
If the Greenland ice sheet melted completely, for example, it would raise global sea levels by seven metres. According to the IPCC report, the melting should take about 1,000 years. But the study, by Tim Lenton of the University of East Anglia, showed the break-up could happen more quickly, in 300 years. Professor Lenton said: "We know that ice sheets in the last ice age collapsed faster than any current models can capture, so our models are known to be too sluggish."
His study identified eight tipping points that could be passed by the end of this century. They include the destruction of the Amazon rainforest, the melting of the west Antarctic ice sheet, and a collapse of the global ocean current known as the thermohaline circulation. If that circulation stopped, the Indian monsoons and the gulf stream could be shut down.
Prof Lenton said the IPCC way of working, including multiple reviews, caused it to issue more conservative reports than his team's studies. He added that the inevitable collapse of the Greenland ice sheet was closer than thought because of the latency in the Earth's climate system. "If you could stabilise the greenhouse gas levels to today's level, you'll still get some further warming [by 2100]."
A global average temperature rise of just 1C would be enough to slip the Greenland ice over the edge. The IPCC's prediction for 2100 is a rise of 1.1C-6.4C.