Thursday, January 3, 2013

Sea levels rising 60% faster than projected: study

by Joe Romm

A new study, “Comparing climate projections to observations up to 2011,” confirms that climate change is happening as fast — and in some cases faster — than climate models had projected. The news release explains:
The rate of sea-level rise in the past decades is greater than projected by the latest assessments of the IPCC, while global temperature increases in good agreement with its best estimates. This is shown by a study now published in the journal Environmental Research Letters. Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research (PIK) and his colleagues compare climate projections to actual observations from 1990 up to 2011. That sea level is rising faster than expected could mean that the Intergovernmental Panel on Climate Change’s (IPCC) sea-level rise projections for the future may be biased low as well, their results suggest.
As Dr Rahmstorf notes, “the new findings highlight that the IPCC is far from being alarmist and in fact in some cases rather underestimates possible risks.”
The oceans are rising 60 per cent faster than the IPCC’s latest best estimates, according to the new research. The researchers compared those estimates to satellite data of observed sea-level rise. ” Satellites have a much better coverage of the globe than tide gauges and are able to measure much more accurately by using radar waves and their reflection from the sea surface,” explains Anny Cazenave from LEGOS. While the IPCC projected sea-level rise to be at a rate of 2 mm per year, satellite data recorded a rate of 3.2 mm per year.
Figure: Sea level measured by satellite altimeter (red with linear trend line) … and reconstructed from tide gauges (orange, monthly data from Church and White (2011))…. The scenarios of the IPCC are shown in blue (third assessment) and green (fourth assessment); the former have been published starting in the year 1990 and the latter from 2000.
The release notes, “The increased rate of sea-level rise is unlikely to be caused by a temporary episode of ice discharge from the ice sheets in Greenland or Antarctica or other internal variabilities in the climate system, according to the study, because it correlates very well with the increase in global temperature.”
As sea level rises, storm surges worsen, coastal populations are put at risk, and salt water infiltrates rich deltas. For more on likely future sea level rise, see “New Studies on Sea Level Rise Make Clear We Must Act Now” and “JPL bombshell: Polar ice sheet mass loss is speeding up, on pace for 1 foot sea level rise by 2050.”
On the subject of global warming, the release explains:

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