So the usual suspects are evidently pissing themselves over the latest, wildly overstated claim that a reduction in sunspot activity will initiate a “mini ice age” and make Al Gore fatter and weepier. Never mind that one of the participants in the relevant study has rejected the wingnut gloss it’s received over the past 24 hours; the larger problem is that AGW doubters insist on citing a hypothesis that has been reluctantly abandoned by one of its original proponents and (for lack of corroborating evidence) ignored or dismissed by nearly everyone else.
Put briefly, climate change “skeptics” often propose an argument based in large part on a small group of studies from the 1990s that subsequent research failed to corroborate. Between 1991 and 1997, two Danish scientists — Eigil Friis-Christensen and Henrik Svensmark — developed a notion that shifts in the intensity of sunspot activity correlate positively with upward or downward shifts in global temperatures. The mechanism for this relationship, they suggested, was a causal link between sunspots and cloud cover. More sunspots, more clouds; more clouds, warmer temperatures. They graphed the data that seemed to validate their hypothesis.
It all sounded plausible, except for the part about the bullshit:
[T]he two key graphs [from Friis-Christensen and Svensmark's work] are based on flawed data. There is no correlation between global warming and solar activity, and no correlation between cloud cover and cosmic rays, the critics say.
The flaws were first identified by Peter Laut, a Danish scientist who was once science adviser to the Danish Energy Agency. Laut, now retired, demonstrated in a study first aired in 2000 and published in a peer-reviewed journal in 2003 that both graphs contained serious errors. When these flaws were corrected, the apparent correlations between global warming and solar activity, and cosmic rays and cloud cover, disappeared.
. . . Six leading experts, including one Nobel laureate, agreed with Laut’s analysis that the graphs of Friis-Christensen and Svensmark showing apparent correlations between global warming, sunspots and cosmic rays are deeply flawed.
Friis-Christensen now accepts that any correlation between sunspots and global warming that he may have identified in the 1991 study has since broken down. There is, he said, a clear “divergence” between the sunspots and global temperatures after 1986, which shows that the present warming period cannot be explained by solar activity alone.
As anyone familiar with the research would tell you, the relationship between sunspot activity and global temperatures is poorly understood. Aside from the the dubious mechanism proposed by Svensmark and others, there does seem to be a measurable (though tiny) correlation between sunspots and overall solar luminosity. But as Joe Romm points out, even if we were looking forward to a “grand minimum” phase of solar activity — a questionable prediction in the first place — the decrease in luminosity would perhaps amount to a reduction of .1 to .3 degrees Celsius. (That’s a decimal point in there, by the way.)
Lacking a stronger mechanism to link solar variation with climate change, it would seem the deniers have only magic and miracles at their disposal. Which I guess explains a lot after all.