A paper co-authored by UA scientist Malcolm Hughes, coming out next week appears to settle the political debate over the so-called 'hockey stick' curve of global warming.
The paper published in the online edition of the Proceedings of the National Academy of Sciences concludes that the northern hemisphere is now warmer than at any time in at least 1300 years.
Hughes, at the UA Laboratory of Tree-Ring Research, lead author Michael Mann, and co-authors examined a wide variety of climate proxy data after controversy arose over the use of tree-ring data to produce the 'hockey stick-shaped' curve showing a dramatic temperature rise in recent years.
The tree-ring data has been controversial due to differences in the thickness of growth rings between young and old trees. The researchers say the large number of other proxies now allow them to derive a long-term temperature record for the Northern Hemisphere without tree-ring data, although data for the Southern Hemisphere is still sparse to date.
In 2006, Congressman Joe Barton of Texas, chairman of the House Energy Committee challenged the hockey stick curve, questioned the credibility and veracity of the scientists involved, and demanded copies of all their data and records. This led to sharply worded concern in the scientific community about a political witch-hunt by climate doubters.