The Greenland icesheet is more sensitive to global warming than thought, for just a relatively small – but very long term – temperature rise would melt it completely, according to a study published today.

Previous research has suggested it would need warming of at least 3.1 degrees Celsius (5.6 degrees Fahrenheit) above pre-industrial levels, in a range of 1.9-5.1 c (3.4-9.1 F), to totally melt the icesheet.

But new estimates, published in the journal nature climate Change, put the threshold at 1.6 c (2.9 F), in a range of 0.8-3.2 c (1.4-5.8 F), although this would have to be sustained for tens of thousands of years.

Greenland is second to Antarctica as the biggest of locked-up water on land. If it melted completely, this would drive up sea levels by 7.2 metres, swamping deltas and low-lying islands.

If global warming were limited to 2 c (3.6 F), a target enshrined in the UN climates-change negotiations, complete melting would happen on a timescale of 50,000 years, according to the study. Current carbon emissions, though, place warming far beyond this objective. If they were unchecked, a fifth of the icesheet would melt within 500 years and all would be gone within 2,000 years, the study says.

The probe is authored by scientists from the Potsdam Institute for Climate Impact Research (PIK) and the Universidad complutense de Madrid.

They say that the risk of total loss may seem remote, given the immense timescale.