On a business-as-usual, high emissions path for CO2, global sea levels will rise 6.8m (22 ft) by 3000 AD. Irreversible warming will cause this trend to continue for thousands more years to come, ultimately reaching 65m (213 ft).
That's the conclusion of a new study published this week in IOP Publishing's journal Environmental Research Letters, which sought to model sea-level changes on very long timescales of millenia, taking into account all of Earth's ice and the warming of the oceans – something which has not been done before.
In all of the scenarios that the researchers analysed, the Greenland ice sheet was responsible for more than half of the rises; thermal expansion of the oceans was the second highest contributor, and the contribution of glaciers and ice was only small.
The researchers believe this is the first study to incorporate glaciers, ice caps, both the Greenland and Antarctic ice sheets and the thermal expansion of the oceans into a comprehensive projection of sea-level rises. They did so by using a modelling system called LOVECLIM, which includes components from a number of different subsystems.
Polar ice sheets are not normally included in projections due to computational constraints and researchers often find it difficult to account for the 200,000 individual glaciers found all over the world in very different climatic settings.
Professor Philippe Huybrechts, co-author of the study: "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. 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 emissions. The lower the ultimate warming will be, the less severe the ultimate consequences will be."
Under the high emissions scenario – which we're currently heading for – vast swathes of inhabited land would be submerged, including many of the world's most famous cities. Firetree.net has a map that uses NASA data and the Google Maps API to simulate future sea level rises.
Of course, this 7 metre rise assumes that no technological solutions will be attempted between now and 3000 AD...