New satellite data which more accurately measures the rate of ice-melt could help us better understand how Antarctica is changing in the light of global warming.
The rate of global sea level change is reasonably well-established but understanding the different sources of this rise is more challenging. Using re-calibrated scales that are able to ‘weigh’ ice sheets from space to a greater degree of accuracy than ever before, a team led by Professor Matt King has discovered that Antarctica overall is contributing much less to the substantial sea-level rise than originally thought.
Instead, the large amount of water flowing away from West Antarctica through ice-melt has been partly cancelled out by the volume of water falling onto the continent in the form of snow, suggesting some past studies have overestimated Antarctica’s contribution to fast-rising sea levels.
Using Gravity Recovery and Climate Experiment (GRACE) satellite data, the team calculated ice sheet mass loss by more accurately mapping and removing the mass changes caused by the flow of rock beneath Earth’s surface.
The team’s findings were published today (Monday 22 October) in the academic journal Nature.
Prof King, who recently joined the University of Tasmania’s School of Geography and Environmental Studies from Newcastle University in the UK, where he conducted the bulk of the research, said the data meant we were at last close to understanding how Antarctica is changing.
“We have tried to weigh the ice in the past but GRACE only measures the combined effect of the ice changes and the land mass changes occurring beneath the Earth’s surface,” he explains. “The step forward we have made is to provide a better calculation of the land mass changes so we can correct the satellite measurements to more accurately calculate the changes in ice mass alone.
“Our ice change calculations rely heavily on how well we can account for these important changes taking place beneath the Earth’s surface. While the land beneath the ice is moving by no more than a few millimetres-per-year – the thickness of a fingernail – that seemingly small effect significantly alters the rate at which we estimate the ice is changing.
“By producing a new estimate of the land motion we’re effectively re-calibrating the scales – in this case the GRACE satellite –so we can more accurately weigh the ice. And what we’ve found is that present sea level rise is happening with apparently very little contribution from Antarctica as a whole.”
Because most of the Antarctic land surface is covered by ice it has been incredibly difficult to determine where it is rising and falling and by how much. That has meant GRACE data hasn’t been able to contribute as much as it could to help scientists understand if Antarctica was growing or shrinking.
“We’re now confident it is shrinking,” says Prof King. “Our new estimate of land motion helps us narrow the range and shifts the best estimate to the lower end of the ice-melt spectrum.
“Worryingly, though, the rate of shrinking has sped up in some important locations. The parts of Antarctica that are losing mass most rapidly are seeing accelerated mass loss and this acceleration could continue well into the future.
“The sea level change we’re seeing today is happening faster than it has for centuries with just a small contribution from the massive Antarctic ice sheet. What is sobering is that sea levels will rise even faster if Antarctica continues to lose increasingly more ice into the oceans.”
Team member Professor Mike Bentley, of Durham University, added: “We have shown that the Antarctic contribution is smaller than some previous estimates, but the ice sheet is changing very rapidly in some key regions”.
The University of Tasmania’s Deputy Vice-Chancellor (Research), Prof Paddy Nixon, said Prof King’s recruitment as a Professor of Polar Geodesy and ARC Future Fellow was a “great example of UTAS’ ability to attract world-class researchers in the field of Antarctic and Southern Ocean studies”.
The research is part of a £600,000 ($940,000) project funded by the UK’s Natural Environment Research Council.