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Sometimes I think the climate debate remains stalled because those who are most concerned refuse to ask the pertinent questions. Instead, they keep refighting old battles that are no longer relevant to a constructive discourse. The latest example is this survey by John Cook et al that is getting a lot of undeserved attention in the mainstream media. I say that because, questionable methodology aside, the survey tells us nothing new and is, as science journalist David Appell noted, a meaningless exercise.
Some of the most extreme predictions of global warming are unlikely to materialise, new scientific research has suggested, but the world is still likely to be in for a temperature rise of double that regarded as safe. The researchers said warming was most likely to reach about 4C above pre-industrial levels if the past decade's readings were taken into account. That would still lead to catastrophe across large swaths of the Earth, causing droughts, storms, floods and heatwaves, and drastic effects on agricultural productivity leading to secondary effects such as mass migration.
Some climate change sceptics have suggested that because the highest global average temperature yet recorded was in 1998 climate change has stalled. The new study, which is published in the journal Nature Geoscience, shows a much longer "pause" would be needed to suggest that the world was not warming rapidly. Alexander Otto, at the University of Oxford, lead author of the research, told the Guardian that there was much that climate scientists could still not fully factor into their models. He said most of the recent warming had been absorbed by the oceans but this would change as the seas heat up. The thermal expansion of the oceans is one of the main factors behind current and projected sea level rises.
The highest global average temperature ever recorded was in 1998, under the effects of a strong El Niño, a southern Pacific weather system associated with warmer and stormy weather, which oscillates with a milder system called La Niña. Since then the trend of average global surface temperatures has shown a clear rise above the long-term averages the 10 warmest years on record have been since 1998 but climate sceptics have claimed that this represents a pause in warming. Otto said that this most recent pattern could not be taken as evidence that climate change has stopped. "Given the noise in the climate and temperature system, you would need to see a much longer period of any pause in order to draw the conclusion that global warming was not occurring," he said. Such a period could be as long as 40 years of the climate record, he said.
Otto said the study found that most of the climate change models used by scientists were "pretty accurate". A comprehensive global study of climate change science is expected to be published in September by the Intergovernmental Panel on Climate Change, its first major report since 2007. Jochem Marotzke, professor at the Max Planck Institute for Meteorology in Hamburg and a co-author of the paper, said: "It is important not to over-interpret a single decade, given what we know, and don't know, about natural climate variability. Over the past decade the world as a whole has continued to warm but the warming is mostly in the subsurface oceans rather than at the surface."
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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. The slowdown in the expected rate of global warming has been studied for several years now. Earlier this year, the UK Met Office lowered their five-year temperature forecast. 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.
The impacts of rising temperature are being felt particularly keenly in the polar regions
Transient nature
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 report suggests that warming in the near term will be less than forecast
"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.
Ocean storage
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.
More BBC News - Climate slowdown means extreme rates of warming 'not as likely'
