Lately, I’m hearing the warmmongers prefer the term “climate change” to global warming. That way, they can claim any change that occurs. However, if you study the Earth’s geologic history, you’ll find that the planet has cooled and warmed many times even predating the existance of human beings. The one thing that seems constant about the climate is that it changes. During the last major ice age less than 20,000 years ago, a significant portion of the northern hemisphere was covered with ice over a mile thick. That ice melted, so obviously the Earth must have warmed. As lwolv pointed out, Greenland was warm enough about 800 years ago to support agriculture. There was also the Little Ice Age that lasted about 500 years, along with other climate cycles over the eons.

There is little reason to doubt that the climate is changing still. The question is whether human activity is responsible for the change, even in part. The evidence to support this is pretty thin. As someone who programmed computers for many years, I know there are lies, damn lies, and computer models. The accuracy of any model is based on how well the developers understand the fundamentals of the domain being modeled. There’s also a question of validation for the results. To validate a climate model, a good approach would be to start at some known set of conditions in the past (say 100 or 500 years ago) and see how well the model reflects what actually happened in the time since. If the model can’t reliably predict what actually happened, how can anyone believe it can accurately predict what might happen in the future?