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.
The study, which has been published today, 28 November, in IOP Publishing's journal Environmental Research Letters, 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 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."
From 28 November, this paper can be downloaded for free from http://iopscience.iop.org/1748-9326/7/4/044035/article
Notes to Editors
1. For further information, a full draft of the journal paper or contact with one of the researchers, contact IOP Press Officer, Michael Bishop:
Tel: 0117 930 1032
Comparing climate projections to observations up to 2011
2. The published version of the paper 'Comparing climate projections to observations up to 2011' (Stefan Rahmstorf et al 2012 Environ. Res. Lett. 7 044035) will be freely available online from 28 November. It will be available at http://iopscience.iop.org/1748-9326/7/4/044035/article
Environmental Research Letters
3. Environmental Research Letters is an open access journal that covers all of environmental science, providing a coherent and integrated approach including research articles, perspectives and editorials.
4. IOP Publishing provides publications through which leading-edge scientific research is distributed worldwide. IOP Publishing is central to the Institute of Physics (IOP), a not-for-profit society. Any financial surplus earned by IOP Publishing goes to support science through the activities of IOP.Beyond our traditional journals programme, we make high-value scientific information easily accessible through an ever-evolving portfolio of community websites, magazines, conference proceedings and a multitude of electronic services. Focused on making the most of new technologies, we're continually improving our electronic interfaces to make it easier for researchers to find exactly what they need, when they need it, in the format that suits them best. Go to http://ioppublishing.org/.
The Institute of Physics
5. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 45,000, working together to advance physics education, research and application. We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications. Go to www.iop.org
Environmental Research Letters