Because the climate has done, what it has always done - it has changed.
Unfortunately there's no money in the fact that the climate has naturally changed since the dawn of time. Governments know they can cash in by saying tiny, puny, insignificant little mankind somewhow has the power to change the climate.
Still, don't stop the believers having something to believe. It used to be religion that would bring about hell and damnation if they didn't toe the line and believe, now it's climate change. Unfortunately the 'believers' are being manipulated by those far more intelligent than them. It keeps simpler types down, but woe betide anyone who dares to point out the emperor's new clothes.