Global warming this century could trigger a runaway thaw of Greenland’s ice sheet and other abrupt shifts such as a dieback of the Amazon rainforest, scientists said on Monday.

They urged governments to be more aware of “tipping points” in nature, tiny shifts that can bring big and almost always damaging changes such as a melt of Arctic summer sea ice or a collapse of the Indian monsoon.

“Society may be lulled into a false sense of security by smooth projections of global change,” the scientists at British, German and U.S. institutes wrote in a report saying there were many little-understood thresholds in nature.

UC Berkeley researchers report that environmental damage caused by rich nations affects poor nations so much, it costs them more than their combined foreign debt.

The study examined the impacts of the expansion of agriculture, deforestation, overfishing, loss of swamps and ozone completion from 1961 to 2000.

When all these impacts are added up, the portion of the footprint of high-income nations falling on low-income countries is greater than their entire financial debt, or about $1.8 trillion, according to lead researcher Thara Srinivasan.

Global warming is partly to blame for the increasing intensity and frequency of massive wildfires in the American West, according to one expert, who says more than half of the region’s forests could be claimed by fire in the next century.

Tom Swetnam, a leading fire ecologist at the University of Arizona, told CBS’s 60 Minutes that a temperature increase in the West of just one degree had contributed to a four-fold increase in fires in the area.

The decade of 1998-2007 is the warmest on record, according to data sources obtained by the World Meteorological Organization (WMO). The global mean surface temperature for 2007 is currently estimated at 0.41°C/0.74°F above the 1961-1990 annual average of 14.00°C/57.20°F.

An already relentless melting of the Arctic greatly accelerated this summer, a warning sign that some scientists worry could mean global warming has passed an ominous tipping point. One even speculated that summer sea ice would be gone in five years.

Greenland’s ice sheet melted nearly 19 billion tons more than the previous high mark, and the volume of Arctic sea ice at summer’s end was half what it was just four years earlier, according to new NASA satellite data obtained by The Associated Press.