I am not denying that we are having more severe weather, higher watermarks on the coast, etc. I am just saying that the evidence I've seen has not really shown to me that it is only man's fault.
Why does it have to be only man's fault? There are so few things in the world that have only a single cause. Isn't the fact that man is apparently contributing to it, enough?
It's true the Earth has experienced many things in the past, including warm periods, ice ages, and mass extinctions. In fact, for most of the Earth's lifetime, it has gotten along fine without humans. Now, I don't expect global warming will make humans extinct, as a group we're pretty adaptable (if you don't care what happens to any particular individuals). But if it's enough, it could, there have been widespread extinction events before. Homo sap has been here for what, 100K years +- 50% (on the long side for critters with the right anatomy, on the short side for behavior), there's no guarantee we will be here for another 100K, or even 10K. Nature doesn't care, any more than it did about dodos or passenger pigeons, we can be replaced.
But even if global warming doesn't mean extinction, flooding, heat, changing weather patterns, changing disease patterns, changing rainfall can mean the deaths of many individuals. We're much more likely to make things worse by not changing our behavior, than we are by changing it to reduce our contribution to warming.