Where ice meets ocean - Antarctic coastline by McKay Savage via Flickr (CC BY 2.0).
Antarctic warmth brings more snow, reducing sea level rise
Alex Kirby & Oliver Tickell
18th March 2015
Rising temperatures will result in more snow falling in Antarctica, and the build-up of ice will reduce sea level rise from other sources. But as the extra weight of ice makes Antarctica's glaciers flow faster, the continent will still be a net contributor to sea level rise.
If we look at the big picture, these new findings don't change the fact that Antarctica will lose more ice than it will gain, and that it will contribute to future sea-level change.
Evidence is mounting that the more the Antarctic warms under the impact of climate change, the more snow will fall on it, causing a build-up of ice.
The research, published in Nature Climate Change, builds on high-quality ice-core data and fundamental laws of physics captured in global and regional climate model simulations.
The team of authors, led by scientists from Germany's Potsdam Institute for Climate Impact Research (PIK), says each degree Celsius of warming in the region could increase Antarctic snowfall by about 5%.
The suggestion that Antarctic snowfall is increasing is not itself new. But what the Potsdam scientists have done is important: they both provide new evidence to support the contention, and explore its potential consequences.
Katja Frieler, climate impacts and vulnerabilities researcher at PIK, and lead author of the report, says: "Warmer air transports more moisture, and hence produces more precipitation. In cold Antarctica, this takes the form of snowfall.
"We have now pulled a number of various lines of evidence together and find a very consistent result: temperature increase means more snowfall on Antarctica."
The answers are in the ice-cores
To reach a robust estimate, the PIK scientists collaborated with colleagues in the Netherlands and the US including co-author Peter U. Clark, professor of geology and geophysics at Oregon State University.
"Ice-cores drilled in different parts of Antarctica provide data that can help us understand the future", he says. "Information about the snowfall spanning the large temperature change during the last deglaciation, 21,000 to 10,000 years ago, tells us what we can expect during the next century."
The researchers combined the ice-core data with simulations of the Earth's climate history and comprehensive future projections by different climate models, and were able to pin down temperature and accumulation changes in warming Antarctica.
The 'good news' is that the increasing snowfall on the continent will add to the mass of the ice sheet and increase its height, offsetting sea level rise from other causes.
But on balance, Antarctica will still lose ice to the ocean
But the 'bad news', say the researchers, is that most of the snow won't stay there. "Snow piling up on the ice is heavy and presses down - the higher the ice, the more pressure", co-author Ricarda Winkelmann explains.
On the basis of another previous PIK study, the extra snow will increase the amount of ice flowing to the ocean. "Because additional snowfall elevates the grounded ice-sheet on the Antarctic continent but less so the floating ice shelves at its shore, the ice flows more rapidly into the ocean and contributes to sea level", says Dr Winkelmann.
So on balance, the sea level-lowering effect from the extra snow is a relatively small one: the 5% increase in Antarctic snowfall that they expect for every 1°C rise in temperature would mean an estimated drop in sea-level of only about three centimetres after a century. By contrast melting ice in Greenland threatens metres of sea level rise.
Adding to Antarctica's contribution to sea level rise, rising sea levels in the Southern Ocean - mainly caused by the thermal expansion of oceans and melting glaciers around the world, most importantly on Greenland - will allow coastal ice shelves to flow more rapidly into the ocean.
Furthermore even slight warming of the waters lapping Antarctica will make it easier for coastal ice to break off, allowing more of the continental ice mass to discharge into the ocean.
So the frozen continent will still be a net source of sea level rise in a warming world, says co-author Anders Levermann - PIK professor of dynamics of the climate system, and lead author of the sea-level rise chapter in the latest report by Intergovernmental Panel on Climate Change.
"If we look at the big picture, these new findings don't change the fact that Antarctica will lose more ice than it will gain, and that it will contribute to future sea-level change", he says.
Dr Frieler agrees: "Under global warming, the Antarctic ice sheet, with its huge volume, could become a major contributor to future sea-level rise, potentially affecting millions of people living in coastal areas."
Alex Kirby writes for Climate News Network.
Oliver Tickell edits The Ecologist.
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