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Sunday, February 04, 2007

Climate change

Friday, Working Group I of the Intergovernmental Panel on Climate Change released "Climate Change 2007: The Physical Science Basis, Summary for Policymakers," which is the first of several parts of the Fourth Assessment Report.

Hundreds of scientists reviewed mountains of research and reported (p. 2) a "very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming." A footnote noted that the italicized phrase meant there was a 9 out of 10 chance of being correct.

Warming itself is described as "unequivocal" (p. 4) Of the 12 warmest years on record since 1850, 11 of them have occurred since 1995.
"Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations" (p. 8).
"Anthropogenic" is a scientist's way of saying "caused by humans." Incidentally, the italicized phrase in this sentence also means greater than 90% probability by the standards used in the report.

Ah, precision!

There's a great deal of potential bad news about melting of ice caps, changed precipitation patterns, likelihood of extreme weather events, future heating of the earth, etc.

In a report filled with unpleasant news, this (p. 8) struck me as especially significant:
"The last time the polar regions were significantly warmer than present for an extended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6 metres of sea level rise."
The debate about the science is over.

The question for policymakers: try to mitigate -- or adapt?

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