Each degree of warming raises sea levels 2.3 metres in the long run, says study
New research has for the first time combined records of past climates and models of the future to estimate how much sea levels will rise even if global temperatures peak. Each degree of global warming could commit earth to 2.3 metres of sea level rise over the next two thousand years, it suggests.
The new modelling shows that the giant ice sheets covering Antarctica and Greenland are likely to be the main drivers of sea level rise in the coming millennia, with mountain glaciers contributing less over time as they shrink. The effect of water expanding as it warms, which is one of the biggest drivers of sea level rise today, is likely to be less important as ice sheet melt speeds up.
Inertia in the system
Air temperatures have responded fairly quickly to rising greenhouse gases, but sea level rise, caused in part by melting ice, happens more slowly.
This means that even if greenhouse gas emissions are cut and temperature rise levels out, sea levels will continue to rise for some time. Lead author of the study, Anders Levermann, neatly summarised:
“The problem is: once heated out of balance, the [oceans and ice sheets] simply don’t stop,”
Using models to examine how the ice sheets covering Greenland and Antarctica could change as the world warms, the scientists on the project were able to demonstrate just how big a threat long lasting sea level rise could be.
Their results suggest that for each degree of global warming, the Earth is committed to 2.3 metres of long term sea level rise:
Long term projections
These projections are quite startling and help illustrate the long term challenge from sea level rise. One of the Intergovernmental Panel on Climate Change’s (IPCC) new low emissions scenarios suggests that if temperatures rise by 2 degrees Celsius, sea levels will rise 0.46m by 2100.
But sea levels will keep rising, Levermann’s research highlights. Eventually – after two millennia – sea levels will rise by a median value of 4.8m.
As with all modelling, the results should be treated carefully. The range in possible outcomes for each degree of temperature rise is wide. Long term sea level rise could be as low as 1m or as high as 4.9m per degree of warming, the authors acknowledge. The models used to estimate ice sheet melt are still fairly new, making even short term predictions of sea level rise quite uncertain.
The authors say they are confident that their estimate is “robust” because of the “combination of physics and data used.” And when the team compared their estimates of sea levels under higher temperatures to similar warm periods in Earth’s past, they found a pretty good match.
2100 too short-sighted
Levermann says that the research shows it’s important to have a longer-term perspective on sea level rise:
“Continuous sea-level rise is something we cannot avoid unless global temperatures go down again. Thus we can be absolutely certain that we need to adapt â?¦ Sea-level rise might be slow on time scales on which we elect governments, but it is inevitable and therefore highly relevant for almost everything we build along our coastlines, for many generations to come.”
Global temperatures have risen 0.8 degrees Celsius since pre-industrial times. According to this modelling that commits us to nearly 2m of long term sea level rise over the next two millennia. Planning and adapting to that will require looking further into the future than the end of the century.