One of the unequivocal "must reads" for those new to - or needing a refresher on - climate change. The author is Spencer R. Weart (e-mail him), director of the Center for History of Physics of the American Institute of Physics (AIP) in College Park, Md. The site, a hypertext history, is a companion piece to Weart's longer Harvard University Press (2003) book of the same title. The site is updated annually.

An opening "summary of the history" of climate change science. From there, things get much more interesting and intriguing. For a taste of where Weart is coming from, consider this excerpt from his "personal note" conclusions:

Faced with scientists who publish warnings, the public's natural response is to ask them for definitive guidance. When the scientists fail to say for certain what will happen, politicians habitually tell them to go back and do more research. That is all very well, but in the case of climate, waiting for a sure answer would mean waiting forever. When we are faced with a new disease or an armed invasion, we do not put off decisions until more research is done. We act using the best guidelines available.

My training as a physicist and historian of science has given me some feeling for where scientific claims are reliable and where they are shaky. Of course climate science is full of uncertainties, and nobody claims to know exactly what the climate will do. That very uncertainty is part of what, I am confident, is known beyond doubt - our planet's climate can change, tremendously and unpredictably. Beyond that we can conclude (with the Intergovernmental Panel on Climate Change in its 2007 report) that it is very likely that significant global warming is coming in our lifetimes. This surely brings a likelihood of harm, widespread and grave (see this summary of expected impacts). The few who contest these facts are either ignorant, or so committed to their viewpoint that they will seize on any excuse to deny the danger.