What was done
The author reviews what is known about the mass balance of the Greenland and Antarctic ice sheets, as well as prospects for resolving remaining uncertainties with the most modern observation methods, using the Greenland ice sheet as an example.

What was learned
The future contribution of the Greenland and Antarctic ice sheets to global sea level depends upon the past climate and dynamic histories of the ice sheets as much as it does upon future climate.  With respect to potential climate change, there is a broad consensus that a 1°C climatic warming would create but little net change in mean global sea level; for Greenland's contribution would be a sea level rise on the order of 0.30 to 0.77 millimeters per year, while Antarctica's contribution would be a fall on the order of 0.20 to 0.70 millimeters per year.  With respect to the impact of past climate change and the ice sheets' consequent dynamic histories, "we do not know," the author says, "whether the ice sheets are currently in balance; neither do we know if their volume or mass has increased or decreased during the last 100 years."

What it means
Each time an iceberg the size of a small state breaks loose from one of the polar ice sheets, we are bombarded by prophecies of impending doom and calls for the crucifixion of people who deal in fossil fuels.  Do some people inherently know what the best measurements of the past and present cannot yet discern?  As the author states, "the new techniques are not capable of directly yielding the long-term background trend of ice sheet mass balance, unless applied over a period of many decades."  Hence, we do not know what is normal or abnormal in this regard; and trying to intimidate fossil fuel consumers every time a big ice cube is spotted floating in the ocean is truly unethical.