A new study by Gael Durand, at Grenoble Alps University, and others shows that the Pine Island Glacier, one of the largest in the Antarctic, is in “irreversible decline”.
The grounding line – the line along which the glacier lifts away from the sea bottom – has receded about six miles since 2003. But that’s just the start according to Durand; the glacier "has started a phase of self-sustained retreat and will irreversibly continue its decline." This conclusion is based on the use of three different models by the authors. The authors expect a five-fold increase in the volume of ice lost from the glacier for the period 2012 to 2031.
This is dramatic but unsurprising. The IPCC reports multiple measures of accelerating change:
· The global mean sea level rose by an average of 1.7 mm per year from 1901-2010 but by 3.2 mm per year between 1993 and 2010.
· Losses from Greenland's ice sheet have probably increased from 34 billion tons per year between 1992 and 2001 to 215 billion tons per year between 2001 and 2010.
· In Antarctica, the rate of loss probably increased from 30 billion tons a year to 147 billion tons a year over the same timescale.
Forecasts of future warming, melting and sea level rise are highly uncertain precisely because the rates are increasing so sharply. It’s no secret that scientists are struggling to understand these changes. What’s not uncertain is that rising sea levels will threaten low-lying communities round the world, starting with the poorest. Without radical change in industry and agriculture the question is not whether they will threaten London and other cities in the developed world but when.