The 1 October article highlights developments in aircraft and satellite techniques that have revolutionised our ability to survey ice sheets, providing accurate measurements of surface elevation, ice thickness, glacier velocity, surface temperatures and snow wetness over vast areas, as well as high-resolution imagery for entire ice sheets.
The new data produced shows that the Greenland and Antarctic ice sheets are shrinking, while floating ice shelves and glacial tongues are not only thinning but breaking up as ocean waters warm and summer air temperature rises.
Moreover, the more glaciers break up, melting gets worse accordingly, due to what Thomas describes as a "loosening the corks", or thinning, effect.
Meanwhile, warmer summers are extending the zone and intensity of melting to higher elevations, Thomas warns, increasing melt-water runoff and lubricating glacier sliding, again speeding up deterioration.
The article evaluates three methods of measuring the rate of change of an ice sheet's mass – its 'mass balance':
- The mass-budget approach, which compares total snowfall with losses from ice discharge and melt-water runoff;
- Repeated altimetry, to estimate volume changes; and;
- Monitoring temporal changes in gravity, to indicate mass changes.
Thomas explains that all three approaches are far from ideal, because for various reasons, small errors in the input data can result in large mass-balance errors.
He concludes that the creation of an international programme to make long-term measurements is urgent and should include the following:
- Early warning of high-latitude changes in surface temperature, snow-melt extent, glacier velocity and ice-shelf break-up.
- Improved ice-thickness surveys.
- Satellite laser and satellite radar altimetry.
- Aircraft surveys of elevation-change rates and ice-thicknesses at "hot spots".
Only then will it be possible to develop a "clear strategy for the measurement and understanding of ice-sheet mass balance", which is "ever more crucial as the planet warms".