New study assesses glacier contributions to sea level rise

Melting glaciers account for one third of observed sea level rise, according to a new study published in Science.

The research, which used multiple satellites and an extensive collection of ground data - was led by Professor Alex Gardner of Clark University and involved the efforts of 16 researchers from 10 countries, including Dr Bert Wouters from the University of Bristol.

Ninety-nine per cent of Earth's land ice is locked up in the massive Greenland and Antarctic ice sheets.  However, the researchers found that the world's other land ice – repositories of the remaining 1 per cent of land ice – contributed just as much to sea level rise as the two ice sheets combined over the period 2003 to 2009

This is the first time scientists have been able to very precisely estimate how much these glaciers, as a whole, are contributing to sea level rise.  Previously, estimates of the recent contribution of glaciers to sea level rise have differed widely.

The study compared traditional ground measurements to satellite data from NASA's Ice, Cloud, and land Elevation Satellite (ICESat) and Gravity Recovery and Climate Experiment (GRACE) missions.  The processing and interpretation of the GRACE satellite observations was carried out by Dr Wouters of Bristol's School of Geographical Sciences with Professor John Wahr of the University of Colorado.

The researchers found that all glacierised regions lost mass between 2003 and 2009, with the biggest ice losses occurring in Arctic Canada, Alaska, coastal Greenland, the southern Andes and the Himalayas. 

In contrast, Antarctica's peripheral glaciers – smaller ice bodies not connected to the main ice sheet – contributed little to sea level rise during that period which differs from previously published estimates for the period 1961-2004 which showed that they accounted for 30 per cent of the global mass loss from glaciers.

Professor Gardner says, "Traditional estimates of glacier mass loss, based solely on field measurements and localized observations, can sometimes overestimate ice loss when the findings are extrapolated over larger regions with few observations, like entire mountain ranges.

"Although ICESat and GRACE each have their own limitations, their estimates of mass change for large glacierised regions agree very well which gives us strong confidence in our results.''

The findings have serious implications for past assessments and, the researchers conclude, a thorough re-examination of past estimates of glacier contributions to sea level rise is needed.

(Paper: A Consensus Estimate of Glacier Contributions to Sea Level Rise: 2003 to 2009 by Gardner et al in Science)