Global warming

Today's issue of Science Magazine has an article reporting that global warming caused a major shift in the foliage of certain regions. In particular, plants from warmer southern areas moved into the Bighorn Basin of Wyoming. More evidence that President Bush not joining the Kyoto Treaty was a big mistake? Perhaps it was caused by evil corporations and Republicans driving Hummers. Before you rush off in your Prius to mail a check to Earth First, read a bit further into the story. "An increase in the planet's temperature 55 million years ago prompted major shifts in plant distribution..." I suppose that if we can blame President Bush for supplying the faulty intelligence which led Bill Clinton to bomb Saddam's nuclear weapons development plant in 1998, we can blame him for causing global warming 55 million years ago. But if global warming happened without any human help millions of years ago, why would we not expect these natural cycles to continue today? If there was evidence that global temperatures are increasing (which there is not) how can we think that man is responsible for it, when it has been happening for millenia?