Bottom line, i reckon, is that most all climate scientists believe man-made global warming is a real problem. If the data and the scientists are to be generally trusted, as they should be until proven untrustworthy, then the position based on the best evidence available is the best reasonable and rational one to take.
The are few things about our physical world as certain as the idea the sun will rise tomorrow as it did yesterday. And there are still those who believe (have proof, in their eyes) that the world is flat.