There are two irresuptible facts:
Greenhouse effect exists. It is required for life on earth. Without it there would be no life on earth.
Greenhouse gasses add to the greenhouse effect. This is also proven.
Now to what extent and what magnitude? Who knows. But we know these two points are true. In addition, we know cardon amounts are greater then ever before, the climate is changing very fast, and that our seasons are becoming more sever. Is the due to global warming? Who knows.
I say yes. Besides, what do we loose if its not true? We makes the air cleaning, everything more renewable, and create new jobs. Thus there is not any good reason to not at least work on reducing greenhouse gasses, as there is no loss.