FAQ - What Changes Climate?

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Is the sun (or cosmic rays) responsible for current warming?

No. Warming in the first half of the 20th century did happen at the same time as increased solar activity. But that hasn’t been the case with the second half. Based on the sun’s output, we would have expected little or no change.

Haven’t the underlying assumptions of reconstructions of Northern Hemisphere temperatures (the so-called "hockey stick diagram") been debunked?

No. In 2008 the National Academy of Sciences published a new paper (see Take Aways and References) by Michael Mann et al. on proxy-based temperature reconstructions. This paper addressed suggestions made in 2006 by a National Research Council study, using a much larger set of data and analysis methods that were validated with model experiments. It confirmed the likelihood that the recently observed temperature increases in the Northern Hemisphere are unusual for at least the last 1,300 years.