Satellite systems designed to track MSL have become increasingly sophisticated. A European satellite system launched in 2002, known as GRACE (Gravity Recovery and Climate Experiment), tracks MSL with an error of less than 1mm. It also measures subtle changes in the gravitational tug exerted by the oceans, as well as by Earth itself.
As far back as 2007 James Hansen of NASA found that, according to data from the Grace system, Greenland and Antarctica are losing around 150 cubic kilometres of ice annually. This rate has doubled in recent years. An additional loss of 60 cubic kilometres of ice from the Southern Antarctic Peninsula represents a significant boost to the total known annual loss.
Sea level rise, in conjunction with the expansion of oceans resulting from a warming planet, must be taken seriously, regardless of where we stand as individuals on the contentious debate about our own contribution to the situation.
As Hansen astutely pointed out in 2007, the IPCC may have been taking an over-cautious line on sea-level rise. I’ll let him have the last word: “We may rue reticence, if it serves to lock in future disasters.”