Nearly two dozen research teams collaborated to study polar ice sheets in Greenland and Antarctica and discovered definitively that they have added 11mm to global sea levels since 1992, melting ever more quickly.
This polar melting added about one-fifth of the overall global sea level rise in this period, contributing 11.1mm overall but with a give or take uncertainty of 3.8mm, such that the figure could be anywhere between 7.3mm and 14.9mm. All the ice sheets’ combined rate of melting has grown since 1992, with Greenland losing five times as much ice now and Antarctica showing about a 50 per cent increase ice loss rate for the last decade.
The results, which bring to an end 20 years of conflicting results, were published in Science. Researchers used data from satellites measuring the surface altitude, glacier flow and the ice mass’s gravitational effect. Erik Ivins of California's Jet Propulsion Laboratory said the 11.1mm are significant.
When you have 11mm of increased sea level, if you compute the amount of mass that's capable of coming on shore during storm surge, it's a lot of mass, he said, according to The Canadian Press. Small changes in sea levels in certain places mean very big changes in the kind of protection of infrastructure you need to have in place.
Lead author of the research, Professor Andrew Shepherd of Leeds University, explained that East Antarctica ice sheet, which is the largest, has acquired more mass due to increased snowfall. Still, the study determined that Greenland, West Antarctica and the Antarctic Peninsula were all losing mass, more than offsetting East Antarctica's gain.
We can now say for sure that Antarctica is losing ice and we can see how the rate of loss from Greenland is going up over the same period as well, he said. We've brought everybody together to produce a single estimate and it turns out that estimate is two to three times more reliable than the last one.
He noted that the figure is in line with climate change predictions.
We would expect Greenland to melt more rapidly because the temperatures have risen, he commented. We would expect West Antarctica to flow more quickly because the ocean is warmer. And we would also expect East Antarctica to grow because there's more snowfall as a consequence of climate warming.
The findings are in line with various forecasts by the UN's Intergovernmental Panel on Climate Change 2007 assessment, and will be considered for the next report due in September 2013.
The next big challenge - now that we've got quite a good understanding of what's happened over the last 20 years - is to predict what will happen over the next century,” said Dr Hamish Pritchard of the British Antarctic Survey. And that is going to be a tough challenge with difficult processes going on in inside the glaciers and ice sheets.”