You can blather on about proof and a shadow of a doubt all you want, but the fucking temperature has been rising for the last 20 years. The overwhelming consensus among academics in the field is that a) Global Warming is real and b) human activity is at least a contributing factor.
You're technically correct that they could be wrong, and we don't have definitive proof. But all indications are that we should do something about this problem. The consequences for being wrong in inaction are billions of lives and untold destruction of civilization as we know it. The consequences for being wrong in action are that we waste some time and money.