by Pallab Ghosh
Science correspondent, BBC News, Monday, 4 February 2008, 22:54 GMT

Many of Earth's climate systems will undergo a series of sudden shifts this century as a result
of human-induced climate change, a study suggests.

A number of these shifts could occur this century, say the report's authors.

They argue that society should not be lulled into a false sense of security by the idea that climate change will be a gradual process.

The work by an international team appears in the Proceedings of the National Academy of Sciences journal.

"Our findings suggest that a variety of tipping elements could reach their critical point within this century under human-induced climate change," he said.

"The greatest threats are tipping of the Arctic sea-ice and the Greenland ice sheet, and at least five other elements could surprise us by exhibiting a nearby tipping point."

The bulk of climate scientists now believe that human induced global warming has begun to affect some aspects of our climate.

Risk assessment

But that change is the start of a series of more dramatic changes if global warming continues, according to a group of more than 50 scientists.

In a formal survey the researchers said that a number of systems that influence the Earth's weather patterns could begin to collapse suddenly if there's even a slight increase in global temperatures.

At greatest risk is arctic sea ice, the Greenland ice sheet and the west Antarctic ice sheet.

The researchers have listed and ranked nine ecological systems that they say could be lost this century as a result of global warming. The nine tipping elements and the time it will take them to undergo a major transition are:

• Melting of Arctic sea-ice (about 10 years)
• Decay of the Greenland ice sheet (about 300 years)
• Collapse of the West Antarctic ice sheet (about 300 years)
• Collapse of the Atlantic thermohaline circulation (about 100 years)
• Increase in the El Nino Southern Oscillation (about 100 years)
• Collapse of the Indian summer monsoon (about 1 year)
• Greening of the Sahara/Sahel and disruption of the West African monsoon (about 10 years)
• Dieback of the Amazon rainforest (about 50 years)
• Dieback of the Boreal Forest (about 50 years)

The paper also demonstrates how, in principle, early warning systems could be established using real-time monitoring and modelling to detect the proximity of certain tipping points.