I would probably put a check mark in the "undecided" column when it comes to the causes of global warming. However, there is a ton of evidence that such climate swings are commonplace when you look outside our perceptual micro-time-line and beyond our modern carbon-dioxide producing capabilities. Even as recently as the middle-age there is plenty of evidence that the earth was in a Little Ice Age. Certainly it stands to reason that a similar natural change could swing us to a warming trend. I do tend to get a little suspicious when people ignore or choose to argue away such indisputable evidence when talking about global warming. Now that it's a high level political quagmire, I believe less of what I hear about it than ever before.

We still don't have a very accurate (rather...agreed upon) way of measuring "the earth's mean temperature" which makes it difficult to look at a chart showing 2 degree rise and get excited about it. Take a look at this chart (which is a little confusing since it puts the current period on the left) that goes back to about 9500 BC. Chart