Why is the idea of climate change controversial?

Actually, the fact that climate is changing is (no-longer) controversial,but what is controversial is whether this is a man-made change.

If people accept the idea of man-made climate change, they would have to make changes in their life-style (less consumption)- and they don't want to do this. This is why even thought the evidence points to it, many people refuse to accept it. The controversy is between the people who do and don't accept it.