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, an international team including a leading Durham University expert, 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 findings published in the academic journal Nature, will increase our understanding of how Antarctica is changing, say the scientists.
Professor Mike Bentley, Department of Geography, Durham University, who was part of the research team, said:
"Sea level is rising globally but our results show that this has been achieved so far with little contribution from the Antarctic ice sheet.
"This project brought together a range of scientists including geologists, geodesists and computer modellers to work out the contribution of the Antarctic ice sheets to global sea level rise. 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."
Professor Matt King, Professor of Polar Geodesy at Newcastle University, said: "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," said Professor 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."
The research is part of a £600,000 project funded by the Natural Environment Research Council (NERC) to investigate the changing mass of the Antarctic Ice Sheet.
Ice sitting on the Antarctic continent at the peak of the last ice age 20,000 years ago forced the rock beneath to deform and slowly flow away. After that time ice levels generally reduced and the rock within the Earth's mantle more than 100km below the surface has been slowly flowing back in. That change affects the GRACE satellites in exactly the same way as ice moving into and out of the continent.
Since their launch in 2002, the GRACE satellites allow scientists to map Earth’s gravity field every 30 days, mapping changes as mass moves around the Earth’s surface as well as below it.