En ny rapport fra FNs klimapanel viser at polene smelter og at prosessen høyst sannsynlig ikke lar seg stanse.

Rapporten skal offentliggjøres i april, men et resyme har lekket ut.

A critical meltdown of ice sheets and severe sea level rise could be inevitable because of global warming, the world’s scientists are preparing to warn their governments. New studies of Greenland and Antarctica have forced a UN expert panel to conclude there is a 50% chance that widespread ice sheet loss «may no longer be avoided» because of greenhouse gases in the atmosphere.

Such melting would raise sea levels by four to six metres, the scientists say. It would cause «major changes in coastline and inundation of low-lying areas» and require «costly and challenging» efforts to move millions of people and infrastructure from vulnerable areas. The previous official line, issued in 2001, was that the chance of such an event was «not well known, but probably very low».

The melting process could take centuries, but increased warming caused by a failure to cut emissions would accelerate the ice sheets’ demise, and give nations less time to adapt to the consequences. Areas such as the Maldives would be swamped and low-lying countries such as the Netherlands and Bangladesh, as well as coastal cities including London, New York and Tokyo, would face critical flooding.

Dette er langt mer dramatiske tall enn det Klimapanelet la frem i en rapport for to uker siden. Der het det at temperaturen vil stige 4 grader i løpet av dette århundret, og at havet vil stige 59 centimeter. Men forskerne hadde ikke tatt med issmeltingen ved polene og Grønlandsisen. Det utgjør en meget stor forskjell.

A final draft of the report’s summary-for-policymakers chapter, obtained by the Guardian, says: «Very large sea level rises that would result from widespread deglaciation of Greenland and West Antarctic ice sheets imply major changes in coastlines and inundation of low-lying areas, with greatest effects in river deltas.

«Relocating populations, economic activity and infrastructure would be costly and challenging. There is medium confidence that both ice sheets would be committed to partial deglaciation for a global average temperature increase greater than 1-2C, causing sea level rise of 4-6m over centuries to millennia.» Medium confidence means about a five in 10 chance.

Climate change: scientists warn it may be too late to save the ice caps