Ms. Madsen’s recent letter (“Climate fear hard to swallow,” Feb. 13) misunderstands the comments by P.J. Polissar and others in “Proceedings of the National Academy of Sciences” (June 13, 2006). They studied four glacial advances that occurred from A.D. 1250-1810 during the Little Ice Age, a time of global cooling. They do indeed conclude that solar activity minima were responsible for those four late Holocene glacial advances. Their conclusions on solar activity, however, addressed only changes during the Little Ice Age, which ended in the 19th century.
Extrapolating to modern climate, they concluded that “estimates of net anthropogenic greenhouse-gas radiative forcing for the next 50 years surpass that of solar forcing in previous centuries, implying that profound climatic impacts can be predicted for tropical montane regions.” That is, human activity is a major component of current climate change.
This is consistent with all accepted models of modern climate change, which indicate that increased solar insolation and anthropogenic greenhouse gases are both causing increases in mean global temperature. Science operates on all available data, not snippets taken out of context.