Infrastructure protectionSea-levels rising faster than IPCC projections

Published 29 November 2012

Sea-levels are rising 60 percent faster than the Intergovernmental Panel on Climate Change’s (IPCC) central projections, new research suggests; the study involved an analysis of global temperatures and sea-level data over the past two decades, comparing them both to projections made in the IPCC’s third and fourth assessment reports

Sea-levels are rising 60 percent faster than the Intergovernmental Panel on Climate Change’s (IPCC) central projections, new research suggests.

These findings, which have been published 28 November in the Institute of Physics’ journal Environmental Research Letters, are timely as delegates from 190 countries descend on Doha, Qatar, for the UN’s 18th Climate Change Conference this week.

The researchers, from the Potsdam Institute for Climate Impact Research, Tempo Analytics, and Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, state that the findings 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.

An IOP release reports that the study involved an analysis of global temperatures and sea-level data over the past two decades, comparing them both to projections made in the IPCC’s third and fourth assessment reports.

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 percent 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.”

— Read more in Stefan Rahmstorf et al., “Comparing climate projections to observations up to 2011,” Environmental Research Letters 7 (27 November 2012): 044035 (doi:10.1088/1748-9326/7/4/044035)

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