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Climate Models ‘Prove’ Human Induced Polar Warming?
A new paper published in Nature Geoscience is being touted as ‘proof,’ by some sections of the media, that polar warming is being caused by humans. For a change, the BBC was a little more conservative about the claims in its reporting, if not the headline, stating that the study “suggests for the first time that there’s a discernable human influence on both the Arctic and Antarctica.”
And,
“The best fit was with models that assumed that human activities including the burning of fossil fuels and depletion of ozone had played a part.”
John Christy, an atmospheric scientist at the University of Alabama, had his say in The Canadian Press: Clouds, for example, can dampen warming in the real world, but he said models have been shown to amplify warming. “They overstate the confidence of what they have in that result because we have too many examples of models that fail,” Christy said from Huntsville. “We have shown that climate models just don’t have the variability that nature provides to us.” Christy too disputed whether the bulk of continental Antarctica is warming, saying that it is, in fact, cooling. The report looks largely at the Antarctic peninsula – which makes up two per cent of the continent – and the eastern and western coastal regions, where they have found warming. The report focuses on temperature changes going back to 1900 and up to the present, but doesn’t include earlier periods when areas in the Arctic were actually warmer than they are today and were not affected by man-made greenhouse gases, said Christy. “Just 1,000 years ago the Arctic was much warmer than it is today so it’s interesting that they would use the term conclusively,” he said. “Natural variability can account for warming since the Arctic has been warmer before.”
I wrote this for Jennifer Marohasy’s blog on 30th May 2008, which is very relevant to the Antarctic:
There is an interesting News Focus story in this week’s Science journal, that helps to confirm the different climate histrories for the East and West Antarctic ice sheets – a phenomenon that persists in modern times:
ANTARCTICA: Freeze-Dried Findings Support a Tale of Two Ancient Climates
A surprising cache of ancient plant material adds evidence for divergent climate histories of the East and West Antarctic ice sheets over the past 14 million years.
Excerpt: These findings appear to be contradictory at first glance, but in fact they buttress an evolving view among scientists that the two major features of the continent, the western and eastern ice sheets, have experienced vastly different climate histories. Data from the Dry Valleys reveals an East Antarctic Ice Sheet that is high, dry, cold, and stable, at least in its central area. And the ANDRILL cores suggest a more volatile West Antarctic Ice Sheet that is subject to the changing temperatures of the sea in which it wades. “It reaffirms the fragility of the West Antarctic Ice Sheet [WAIS] and the stability of the central part of the East Antarctic Ice Sheet,” says Peter Barrett, a sedimentologist at the Victoria University of Wellington (VUW) in New Zealand, who advised the ANDRILL project.
Ozone hole science isn’t settled either, as I pointed out in another post on Jennifer Marohasy’s blog on 27th September 2007:
New Research Challenges Established Ozone Hole Theory
See also Climate Research News: Winds are Dominant Cause of Greenland and West Antarctic Ice Sheet Losses
November 2nd, 2008 at 7:35 pm
The study “Attribution of polar warming to human influence” was hyped by a multitude of blogs a few days ago, including those at nature, newscientist, dailymail, and telegraph. I, of course, had to comment. My comments at newscientist and the telegraph were posted. Nature and the dailymail elected to delete them. The curious deletion was at Nature since my comment was simply a question to the author. She had noted that “Their method was based on state-of-the-art models of the polar climates that either incorporated anthropogenic as well as natural influences on variability, or included natural factors only. (Human influences include greenhouse gases that cause warming and a cooling effect from depletion of stratospheric ozone; natural ones are solar variation and volcanic eruptions.)”
In my comment, I asked Anna Barnett if solar variation and volcanic eruptions were the only natural variations included in the GCMs. The reason for my question is simple. Here’s a one of my comments at the other blogs to illustrate:
Temperature data contradicts the claims made in the article. The first is a graph of global, Northern Hemisphere, and Arctic land and sea surface temperature anomalies. Note how the Arctic diverges from the global and Northern Hemisphere data after the 97/98 El Nino. Arctic temperatures then remain at the elevated level due to the influence of the subsequent El Nino events that occurred in 2002/03, 2004/05, and 2006/07. Arctic warming in response to El Nino events is consistent with the projections of coupled GCMs and with past climatological records.
http://i34.tinypic.com/2cxasl3.jpg
The second graph is of the Sea Surface Temperature (SST) anomalies for the Southern Ocean, the ocean that surrounds the Antarctic. Southern Ocean SST anomalies have been decreasing since the 1980s.
http://i37.tinypic.com/315bzad.jpg
Sources:
http://bobtisdale.blogspot.com/2008/07/polar-amplification-and-arctic-warming.html
http://bobtisdale.blogspot.com/2008/09/ersstv3-version-of-southern-ocean-sst.html
Regards
Bob Tisdale