Millions of years ago, the planet was warmer than it is now. There weren't polar ice caps and North America was a tropical forest. But after several hundred thousand years of global cooling, the climate in North America changed and reptiles and amphibians underwent changes (in most cases becoming smaller) or they perished.   Mammals were relatively unchanged because of a mammal's ability to regulate its own body temperature.  This is an interesting article and points out that we don't know what the correct temperature for our planet is, so how can we know that the warming trend now is bad?

There is a link in this article to facts about global warming.  The debate rages on. And I will continue to follow it with interest and concern and in the meantime try to do my part to be more planet friendly.