Climate slowdown means extreme rates of warming 'not as likely'
- 19 May 2013
- From the section Science & Environment
Scientists say the recent downturn in the rate of global warming will lead to lower temperature rises in the short-term.
Since 1998, there has been an unexplained "standstill" in the heating of the Earth's atmosphere.
Writing in Nature Geoscience, the researchers say this will reduce predicted warming in the coming decades.
But long-term, the expected temperature rises will not alter significantly.
But this new paper gives the clearest picture yet of how any slowdown is likely to affect temperatures in both the short-term and long-term.
An international team of researchers looked at how the last decade would impact long-term, equilibrium climate sensitivity and the shorter term climate response.
Climate sensitivity looks to see what would happen if we doubled concentrations of CO2 in the atmosphere and let the Earth's oceans and ice sheets respond to it over several thousand years.
Transient climate response is much shorter term calculation again based on a doubling of CO2.
The Intergovernmental Panel on Climate Change reported in 2007 that the short-term temperature rise would most likely be 1-3C (1.8-5.4F).
But in this new analysis, by only including the temperatures from the last decade, the projected range would be 0.9-2.0C.
"The hottest of the models in the medium-term, they are actually looking less likely or inconsistent with the data from the last decade alone," said Dr Alexander Otto from the University of Oxford.
"The most extreme projections are looking less likely than before."
The authors calculate that over the coming decades global average temperatures will warm about 20% more slowly than expected.
But when it comes to the longer term picture, the authors say their work is consistent with previous estimates. The IPCC said that climate sensitivity was in the range of 2.0-4.5C.
This latest research, including the decade of stalled temperature rises, produces a range of 0.9-5.0C.
"It is a bigger range of uncertainty," said Dr Otto.
"But it still includes the old range. We would all like climate sensitivity to be lower but it isn't."
The researchers say the difference between the lower short-term estimate and the more consistent long-term picture can be explained by the fact that the heat from the last decade has been absorbed into and is being stored by the world's oceans.
Not everyone agrees with this perspective.
Prof Steven Sherwood, from the University of New South Wales, says the conclusion about the oceans needs to be taken with a grain of salt for now.
"There is other research out there pointing out that this storage may be part of a natural cycle that will eventually reverse, either due to El Nino or the so-called Atlantic Multidecadal Oscillation, and therefore may not imply what the authors are suggesting," he said.
The authors say there are ongoing uncertainties surrounding the role of aerosols in the atmosphere and around the issue of clouds.
"We would expect a single decade to jump around a bit but the overall trend is independent of it, and people should be exactly as concerned as before about what climate change is doing," said Dr Otto.
Is there any succour in these findings for climate sceptics who say the slowdown over the past 14 years means the global warming is not real?
"None. No comfort whatsoever," he said.
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