Substantial loss of ice-sheet mass has been confirmed for Greenland and West Antarctica, thanks to an innovative approach to data interpretation. The satellite data also showed that the contribution of the receding ice sheets to sea-level rise has accelerated over the past few years.
In 2002, twin satellites were launched to make detailed measurements of Earth’s gravitational field. Variations in the mass of the polar ice sheets — and more generally in the storage of water or ice on land — affect the gravitational field, and this is detected by the GRACE satellites.
The satellite data is complicated to interpret because melting ice isn’t the only cause of gravity changes. To make an accurate estimate of ice-sheet reduction, factors such as changes in oceanic and atmospheric distribution have to be disentangled.
These new findings confirm the ongoing shrinkage of the polar ice sheets. However, the newly estimated ice-sheet mass losses are less than half of other recent GRACE-based estimates for the same time period. This suggests we have previously assumed that ice melting has more of a role in the changes in the gravitational field than it actually does – that’s why reanalysis of the same satellite data produced a different result.
The difference is that the latest studies used ground-based GPS data to reduce their reliance on deglaciation models. This extra data should increase the accuracy of estimates, but they suffer from the problem that there aren’t yet enough measurements. However, the network of GPS sites in Greenland and Antarctica has been considerably expanded since 2007 as part of an International Polar Year project. This will help improve our understanding of the polar ice sheets, and ensure measurements are increasingly accurate.
Bromwich DH & Nicolas JP (2010) Sea-level rise: Ice-sheet uncertainty Nature Geoscience doi:10.1038/ngeo946
GRACE satellites www.csr.utexas.edu/grace
Technological advances increase our knowledge of climate change. Does this mean what we ‘know’ about the climate isn’t accurate enough to go on? Or does it mean we should focus technology on dealing with the problem not just finding out more about it?