‘Official’ IPCC sea level estimates may be too low
By Bob Berwyn
FRISCO — Although Antarctica’s vast ice sheets are only a small factor in global sea level rise right now, that’s likely to change in coming decades, scientists said after a new analysis of ocean temperatures around the frozen continent.
“If greenhouse gases continue to rise as before, ice discharge from Antarctica could raise the global ocean by an additional 1 to 37 centimeters in this century already,” says lead author Anders Levermann, with the Potsdam Institute for Climate Impact Research. “Now this is a big range – which is exactly why we call it a risk: Science needs to be clear about the uncertainty, so that decision makers at the coast and in coastal megacities like Shanghai or New York can consider the potential implications in their planning processes,” says Levermann.
The scientists analyzed how rising global mean temperatures resulted in a warming of the ocean around Antarctica, thus influencing the melting of the Antarctic ice shelves. The marine ice sheets in West Antarctica alone have the potential to elevate sea level by several meters – over several centuries.
According to the study, the computed projections for this century’s sea level contribution are significantly higher than the latest IPCC projections on the upper end. Even in a scenario of strict climate policies limiting global warming in line with the 2 degree Celsius target, the contribution of Antarctica to global sea level rise covers a range of 0 to 23 centimeters.
“Rising sea level is widely regarded as a current and ongoing result of climate change that directly affects hundreds of millions of coastal dwellers around the world and indirectly affects billions more that share its financial costs,” said co-author Robert Bindschadler from the NASA Goddard Space Flight Center.
“This paper is a critical input to projections of possible future contributions of diminishing ice sheets to sea level by a rigorous consideration of uncertainty of not only the results of ice sheet models themselves but also the climate and ocean forcing driving the ice sheet models,” Bindschadler said. “Billions of Dollars, Euros, Yuan etc. are at stake and wise and cost-effective decision makers require this type of useful information from the scientific experts.”
While the study signifies an important step towards a better understanding of Antarctica in a changing climate and its influence on sea level change within the 21st century, major modeling challenges still remain: Datasets of Antarctic bedrock topography, for instance, are still inadequate and some physical processes of interaction between ice and ocean cannot be sufficiently simulated yet.
Notably, the study’s results are limited to this century only, while all 19 of the used comprehensive climate models indicate that the impacts of atmospheric warming on Antarctic ice shelf cavities will hit with a time delay of several decades. “Earlier research indicated that Antarctica would become important in the long term,” says Levermann. “But pulling together all the evidence it seems that Antarctica could become the dominant cause of sea level rise much sooner.”