From The Guardian:
Apparent pause in global warming blamed on 'lousy' data
European Space Agency scientist says annual sea level rises since 1993 indicate that warming has continued unabated
The belief that global
warming has paused is based on the stability of surface temperatures
over the past 15 years. Photograph: Image Source/REX
A widely reported "pause" in global warming may be an artefact of scientists looking at the wrong data, says a climate scientist at the European Space Agency.
Global average surface temperatures rose rapidly from the 1970s but have been relatively flat for the past 15 years. This has prompted speculation from some quarters that global warming has stalled.
Now, Stephen Briggs from the European Space Agency's Directorate of Earth Observation says that surface air temperature data is the worst indicator of global climate that can be used, describing it as "lousy".
"It is like looking at the last hair on the tail of a dog and trying to decide what breed it is," he said on Friday at the Royal Society in London.
Climate scientists have been arguing for some time that the lack of rising temperatures is due to most of the extra heat being taken up by the deep ocean. A better measure, he said, was to look at the average rise in sea levels. The oceans store the vast majority of the climate's heat energy. Increases in this stored energy translate into sea level rises.
"Sea level is a very good integrator of different indicators of climate change," said Briggs.
In the past 50 years, ocean temperature has indicated that the stored energy has increased by 250 zetajoules, he said. A zetajoule is 1021 joules. For comparison, mankind generates 0.5 zetajoules of energy every year in its power stations.
Since 1993, satellites have measured sea levels rising by an average of 3mm per year. Unlike the surface air temperature, this rise continued throughout the supposed pause in global warming.
Christopher Merchant at the University of Reading has been working to understand why the increase in the stored energy has not translated into an increase in surface temperature.
"There are a number of contributions and a picture is emerging," he says. Those contributions include the cooling effect of aerosols from Asian industrialisation, natural variability in the climate system and solar variability.
In March, climate scientists identified another potentially important contribution. The trade winds across the Pacific have strengthened in the past decade, which could be helping to drive a deep circulation of water that traps heat in the depths of the ocean, leaving the surface relatively unaffected for now.
Scientists are now trying to simulate the behaviour using computer models. This is difficult because the behaviour of the deep ocean is too poorly known to be reliably included.
"The models don't have the skill we thought they had. That's the problem," said Peter Jan van Leeuwen, director of the National Centre of Earth Observation at the University of Reading....MORE
