Scientists at an Arctic tipping point conference in Norway are trying to agree terms for an early warning system that could monitor sudden climate shifts, such as the much-feared melting of glaciers.
If the Greenland ice sheet melted completely it would raise global sea levels by about seven metres, and leave many of the world's coastal cities underwater.
"We need leading indicators to see when we are approaching a threshold so that we can stop before we reach it," Carlos Duarte, a professor at the Spanish Council for Scientific Research, told the conference.
The hottest topic on the agenda was how to identify dangerous signs of instability – such as melting glaciers or a disappearance of Arctic sea ice in summer.
A 2009 study in the journal 'Nature' showed that many systems, ranging from ocean currents, wildlife populations or even financial markets, often show signs of increased variability before radical shifts.
The problem is deciding what to watch.
"We have an enormous capacity to collect data, but not an enormous capacity to determine which of those data are the most relevant," Oran Young of the University of California, Santa Barbara, said of the Arctic climate.
"Our challenge is to think of a small number of indicators," he added.
Unusual variability may be the best single sign. Climate scientists have found that there were short-term shifts between warm and cold before the Ice Age ended 10,000 years ago.
Other signs could include changes in correlations – for instance how far rising temperatures match a decline in sea ice extent. As ever more reflective ice melts, it exposes water which soaks up more of the sun's energy, hastening a thaw.
Duarte said the Arctic Ocean might be ice-free in summers from 2020. "We are just about to go across this tipping point," he said.
According to Stefan Rahmstorf, of the Potsdam Institute for Climate Impact Research, recent studies indicate that temperature rises of between 1.3 and 2.3 degrees Celsius might trigger a runaway thaw.
Almost 200 governments agreed last month in Cancún, Mexico, to a goal of limiting the average rise in world temperatures to below two degrees Celsius. But temperatures have already gained by 0.8 degrees Celsius.
"Greenland shows that two degree target may not be enough," Rahmstorf said. As yet, the curbs on greenhouse gas emissions agreed by major emitters are unlikely to meet even this target.
(EURACTIV with Reuters.)