Shepherd et al.: Science 30 November 2012: Vol. 338 no. 6111 pp. 1183-1189 DOI: 10.1126/science.1228102:
We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth’s polar ice sheets. We find that there is good agreement between different satellite methods—especially in Greenland and West Antarctica—and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by –142 ± 49, +14 ± 43, –65 ± 26, and –20 ± 14 gigatonnes year−1, respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter year−1 to the rate of global sea-level rise.
Aunty says Sea-level rise from polar ice melt finally quantified but then immeadiately backs off to the most definitive assessment so far, which seems more accurate. In case you can’t read the abstract, they’re saying that only E Ant is gaining mass, and that at a low rate, so overall Ant is losing, and Greenland is losing even more. Still – that adds up to 0.6 mm/yr. So it will have to grow if its to become interesting by 2100. And undoubtedly it will, but that means predicting it remains interesting, since (linear) extrapolation is obviously pointless.
Oh go on then, I’ll say a bit more. Quoting Aunty:
The lead author of the research, Prof Andrew Shepherd of Leeds University, said the study brought to an end 20 years of disagreement between different teams.
“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 added.
“Prior to now there’d been 30 to 40 different estimates of how the ice sheets are changing, and what we realised was that most people just wanted one number to tell them what the real change was.
“So 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.”
I’m not sure that “most people just wanted one number so we gave them what we wanted” is a good argument. Not having read the paper, I don’t know how they converted multiple numbers into one (by James’s barometer-dropping perhaps? By actually trying to work out why they differed? Either of those would make sense).