Science has found clear records of climate shifts over decades, millenia and eons. Even written history and oil paintings, both relatively recent media, show that Europe has been both hotter and much colder than it is now. I've seen 16th Century paintings showing all the canals in Amsterdam frozen over, and with horse sleighs on the ice. Can't do that today.
Here's one writer arguing that we humans are being foolish to think we can alter climate change. Yet there are always counter-arguments that even small scale change by individuals can matter. In South Asia some agronomists are arguing that we can prepare by preserving those food plants that do well in dry conditions. Here's one of many arguments I've seen for preparing to meet the consequences of a warming earth. Forget prevention that requires 200 nations to co-operate, or at least the twenty biggest economies. This argument goes: get ready to roll with the punches, if and when warming changes ocean levels, weather and agricultural production.
Three incontrovertible truths about climate change: 1) Climate change happens on earth, repeatedly. 2) Never has the human race used digital technology, broad communications, global political effort and massive amounts of money to co-operatively face any global issue. If global warming is happening and humans react, it will take many hundreds of times as much money and effort as, say, innoculation against H1N1 flu. 3) Our knowledge of our planet's climate systems is incomplete and our ability to predict what'll happen, or when, is less than perfect. This is all about probabilities, similar to medical treatment of an individual human. Nothing is going to be 100% all the time. And any climate change is not going to be a linear process. [poll id="212"]