John Cook has an excellent post on his site Skeptical Science that asks (and answers) the question, What does Solar Cycle Length tell us about the sun’s role in global warming?:
Solar cycle length is a useful indicator of long term changes in solar activity. When the sun gets hotter, we observe shorter solar cycles. When the sun shows a long term cooling trend, solar cycle length is longer. A 1991 study by Friis-Christensen and Lassen smoothed out data on solar cycle length and compared it to Northern Hemisphere temperature (Friis-Christensen 1991). The authors suggested the close correlation between solar cycle length and temperature supports the direct influence of solar activity on climate over the past 130 years. Note in particular the close correlation after 1980 during the modern global warming trend.
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In 1999, one of the co-authors of the original 1991 paper updated their analysis with the latest data (Lassen 1999). They found that the solar cycle length showed no trend in the last few decades of global warming. They concluded that “since around 1990 the type of Solar forcing that is described by the solar cycle length model no longer dominates the long-term variation of the Northern hemisphere land air temperature”.
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Claims that solar cycle length prove the sun is causing global warming are based on a single paper published nearly 20 years ago. Subsequent research, including a paper by a co-author of the original 1991 paper, finds the opposite conclusion. Solar cycle length as a proxy for solar activity tells us the sun has had very little contribution to global warming since 1975. In fact, direct measurements of solar activity indicate the sun has had a slight cooling effect on climate in recent decades while global temperatures have been rising.
Of course, this won’t slow down the bogus claims to the contrary from the usual suspects, firmly ensconced in their reality distortion fields.
And while I have the chance, let me suggest that you check John’s site regularly or avail yourself of his RSS feed in Google Reader or other news feed app. He does terrific work and deserves all the readers he can get.
