"Although correlations often can be found, the mechanism behind these correlations is a matter of speculation. Many of these speculative accounts have fared badly over time, and in a paper "Solar activity and terrestrial climate: an analysis of some purported correlations" (J. Atmos. and Solar-Terr. Phy., 2003 p801–812) Peter Laut demonstrates problems with some of the most popular, notably those by Svensmark and by Lassen (below). Damon and Laut report in Eos[21] that the apparent strong correlations displayed on these graphs have been obtained by incorrect handling of the physical data. The graphs are still widely referred to in the literature, and their misleading character has not yet been generally recognized.
In 1991, Knud Lassen of the Danish Meteorological Institute in Copenhagen and his colleague Eigil Friis-Christensen found a strong correlation between the length of the solar cycle and temperature changes throughout the northern hemisphere. Initially, they used sunspot and temperature measurements from 1861 to 1989, but later found that climate records dating back four centuries supported their findings. This relationship appeared to account for nearly 80 per cent of the measured temperature changes over this period (see graph[39]). Damon and Laut, however, show that when the graphs are corrected for filtering errors, the sensational agreement with the recent global warming, which drew worldwide attention, has totally disappeared. Nevertheless, the authors and other researchers keep presenting the old misleading graph.[21] Note that the prior link to "graph" is one such example of this.
Sallie Baliunas, an astronomer at the Harvard-Smithsonian Center for Astrophysics, has been among the supporters of the theory that changes in the sun "can account for major climate changes on Earth for the past 300 years, including part of the recent surge of global warming."[40]
On May 6, 2000, however, New Scientist magazine reported that Lassen and astrophysicist Peter Thejll had updated Lassen's 1991 research and found that while the solar cycle still accounts for about half the temperature rise since 1900, it fails to explain a rise of 0.4 °C since 1980. "The curves diverge after 1980," Thejll said, "and it's a startlingly large deviation. Something else is acting on the climate.... It has the fingerprints of the greenhouse effect."[41]"
