Whatever we do, greenhouse gas emissions have alreadytriggered an irreversible warming of Earth that will cause sea levels to rise for more than a thousand years to come, claims a European team.
The researchers modeled sea-level changes over millennial timescales, for the first time taking into account all of Earth's land ice and the warming of the oceans.
And, they say, whatever happens now, we've already committed ourselves to a sea-level rise of 1.1 metres by the year 3000 as a result of greenhouse gas emissions up to now. Depending on what happens now, things could be worse.
If we follow the high A2 emissions scenario adopted by the Intergovernmental Panel on Climate Change (IPCC), says the team, seas would rise by 6.8 metres over the next thousand years. The two other IPCC scenarios analysed by the researchers, the B1 and A1B scenarios, give sea-level rises of 2.1 and 4.1 metres respectively.
"Ice sheets are very slow components in the climate system; they respond on time scales of thousands of years," says co-author of the study Professor Philippe Huybrechts.
"Together with the long life-time of greenhouse gases in the atmosphere, this inertia is the real poison on the climate system: anything we do now that changes the forcing in the climate system will necessarily have long consequences for the ice sheets and sea level."
In every scenario analysed, the Greenland ice sheet was responsible for more than half of the sea level rises; thermal expansion of the oceans was the second highest contributor, and the contribution of glaciers and ice was only small.
"Ultimately the current polar ice sheets store about 65 metres of equivalent sea level and if climatic warming will be severe and long-lasting all ice will eventually melt," says Huybrechts.
"Mankind should limit the concentration of greenhouse gases at the lowest possible level as soon as possible. The only realistic option is a drastic reduction of the emissions."