You're right, seeing global warming in the past doesn't disprove man-made global warming. However, it does disprove the claim that the temperature changes we're seeing now are unprecedented.<p>But that's exactly what makes me skeptical about man-made global warming. This persistent attempt to make it appear more dramatic and less uncertain than it really is. It's exactly what we saw with weapons of mass destruction not long ago.<p>I'm not saying man-made global warming isn't real, it may well be, but even if it were real there's still the question of costs and benefits. I don't buy the economics as laid out in the Stern review (<a href="http://en.wikipedia.org/wiki/Stern_Review" rel="nofollow">http://en.wikipedia.org/wiki/Stern_Review</a>). We just don't have the scientific methods to make long term predictions for complex systems.