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Fri Apr 26, 2013, 10:35 PM

Nature Geosciences Study Supports Mann's "Hockey Stick" - And Even The Torygraph Concedes


The latest study, published in Nature Geoscience this week, is a truly massive affair, produced by 78 scientists from 24 countries and using data from 511 locations across the globe. It confirmed that there had been an overall cooling trend over the last 2000 years, succeeded by a rapid increase, not just over the world as a whole, but in almost all its regions (Antarctica was the exception and there was not enough information for Africa). It added: “generally the longer the proxy record, the more likely it is to exhibit a significant long-term cooling trend”.

They scientists did confirm that the Northern Hemisphere been a warm period in the Middle Ages, something much cited by sceptics as evidence that the present warming is not unprecedented, but – significantly found that it did not affect the southern Hemisphere at the same time, suggesting it was not, as now, a global effect. They concluded that the “pre-industrial cooling trend was likely caused by natural factors that continued to operate through the 20th century, making the 20th century warming more difficult to explain without the likely impact of increased greenhouse gases”.

Of course sceptics have descended on the study to try to pick holes in it, so the arguments will continue to run and run. But, both sides seem to attach much importance to the hockey stick graph. What went on over the last two thousand years in no way proves that the present warming is caused by human activities; and nor would this be disproved by demonstrating that similar warming had occurred long before people began polluting the atmosphere. Similar elements can have different causes. Natural factors have certainly been responsible for past changes in the climate; the world, for example, was much hotter than it is now hundreds of thousands of years ago. But to contend that this rules out the possibility that humanity is causing the rest warming is like insisting that arsonists cannot cause a forest fire because they have occurred naturally in the past.

What is important is what is happening now. The warming over the last century is undeniable, even if its rate of increase has slowed recently and pollution – by black carbon as well as carbon dioxide and other greenhouse gases, as I have been pointing out for some years – remains overwhelmingly the likeliest cause of it.



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