The fact that tree-ring records do not capture recent warming adds to the scepticism about the value of such records.

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The download on the Mac took about 30 minutes and then I saw on my Mac the familiar tree-ring background.

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And the idea of anthropogenic climate change rests on a great deal more than just tree-ring records, useful as they are for providing context to the current warming.

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Using it, he has built up a series of tree-ring chronologies from Thailand and Vietnam that indicate a period of severe drought across mainland South-East Asia in the early 1400s.

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Such tree-ring records, along with other so-called proxy archives, can provide a wealth of information about volcanic events and their varying impacts around the globe because of resulting shifts in atmospheric circulation and other climate changes, dating for centuries prior to the period of instrumental record.

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Comments on the tree-ring section of the IPCC's latest report by John Mitchell, director of climate science at Britain's Met Office, raise issues very like those highlighted by perhaps the most prominent critic of the hockey stick, Steve McIntyre, who runs a blog called Climate Audit.

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In North America, Laki has been blamed for the starvation of Inuit populations from severe cold in northwestern Alaska, based on Inuit oral history as well as tree-ring density data investigated by Gordon Jacoby and others, who estimated that conditions were about 4 degrees Celsius colder than the mean.

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Take tree ring-based climate reconstructions in the third IPCC report.

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On the horizon are the crater walls, now a ring of tree-covered mountains and national parks.

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