News in Science

Glacier melt causes third of sea-level rise

Big melt Water from the world's shrinking glaciers was responsible for almost a third of the rise in sea levels between 2003 and 2009, shows new research.

An international team of scientist compared data gleaned from two NASA satellites as well as traditional ground measurements from glaciers around the world.

Their work, published in the journal Science , is the most accurate estimation of how glaciers contribute to sea level rises to date.

"For the first time, we've been able to very precisely constrain how much these glaciers as a whole are contributing to sea rise," says lead author Assistant Professor Alex Gardner, assistant geography professor at Clark University in Worcester, Massachusetts.

"These smaller ice bodies are currently losing about as much mass as the ice sheets."

The most significant ice losses occurred in Arctic Canada, Alaska, coastal Greenland, the southern Andes and the Himalayas, the study found.

The glaciers outside of the Greenland and Antarctic sheets lost an average of roughly 260 billion metric tons of ice annually during the period, leading to a rise in ocean levels of about 0.7 millimeters per year.

By contrast the glaciers in Antarctica, smaller ice masses that are not connected to the ice sheet, made scarcely any contribution to sea-level rise over the study period.

"Because the global glacier ice mass is relatively small in comparison with the huge ice sheets covering Greenland and Antarctica, people tend to not worry about it," says Tad Pfeffer, a glaciologist of the University of Colorado at Boulder.

"But it's like a little bucket with a huge hole in the bottom: it may not last for very long, just a century or two, but while there's ice in those glaciers, it's a major contributor to sea level rise."

Scientists estimate that if all the glaciers in the world were to melt, sea levels would rise by about 60 centimetres.

However if the entire ice sheet of Greenland were to vanish, the oceans would surge by six metres. If the Antarctic lost its ice cover, levels would rise about 60 metres.

The study used data from NASA's Ice, Cloud and Land Elevation Satellite, or ICESat, and the Gravity Recovery and Climate Experiment, or GRACE.

ICESat, which ceased operation in 2009, tracked glacier changes by bouncing laser pulses off the surface to calculate the shifting height of ice cover.

The GRACE system works by monitoring variations in Earth's gravity field caused by shifts in the planet's mass distribution, including displacements of ice.

"Because the two satellite techniques are subject to completely different types of errors, the fact that their results are in such good agreement give us increased confidence in those results, says study author Professor John Wahr, also from the University of Colarado.