Sea levels are rising 60
per cent faster than the Intergovernmental Panel on Climate Change's (IPCC)
central projections, new research suggests.
While temperature rises
appear to be consistent with the projections made in the IPCC's fourth
assessment report (AR4), satellite measurements show that sea levels are
actually rising at a rate of 3.2 mm a year compared to the best estimate of 2
mm a year in the report.
The researchers, from the Potsdam Institute for Climate Impact Research, Tempo Analytics and Laboratoire d'Etudes en Géophysique et Océanographie Spatiales, believe that findings such as these are important for keeping track of how well past projections match the accumulating observational data, especially as projections made by the IPCC are increasingly being used in decision making.
Results were obtained by
taking averages from the five available global land and ocean temperature
series.
After removing the three
known phenomena that cause short-term variability in global temperatures --
solar variations, volcanic aerosols and El Nino/Southern Oscillation -- the
researchers found that the overall warming trend at the moment is 0.16°C per
decade, which closely follows the IPCC's projections.
Satellite measurements
of sea levels showed a different picture, however, with current rates of
increase being 60 per cent faster than the IPCC's AR4 projections.
Satellites measure
sea-level rise by bouncing radar waves back off the sea surface and are much
more accurate than tide gauges as they have near-global coverage; tide gauges
only sample along the coast. Tide gauges also include variability that has
nothing to do with changes in global sea level, but rather with how the water
moves around in the oceans, such as under the influence of wind.
The study also shows
that it is very unlikely that the increased rate is down to internal
variability in our climate system and also shows that non-climatic components
of sea-level rise, such as water storage in reservoirs and groundwater
extraction, do not have an effect on the comparisons made.
Lead author of the
study, Stefan Rahmstorf, said: "This study shows once again that the IPCC
is far from alarmist, but in fact has under-estimated the problem of climate
change. That applies not just for sea-level rise, but also to extreme events
and the Arctic sea-ice loss."
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Journal Reference:
1. Stefan Rahmstorf, Grant Foster, Anny Cazenave.Comparing
climate projections to observations up to 2011. Environmental
Research Letters, 2012; 7 (4): 044035 DOI: 10.1088/1748-9326/7/4/044035
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Institute of Physics
(2012, November 27). Sea levels rising faster than IPCC projections. ScienceDaily.
Retrieved November 28, 2012, from http://www.sciencedaily.com/releases/2012/11/121128093911.htm