Greenhouse gas theory is settled and CO2 increases will cause some slight warming. Manmade CO2 releases cause most of the observed atmospheric CO2 increases. But that's as far as the science can go because weather controls climate, not vice versa, and the sun mostly controls weather and not greenhouse gases. The most likely case is that weather will attenuate greenhouse gas changes.
They WANT to believe it.
It gives the politicians power,
and it gives the people a religion, some reason to matter.
Then why was the CO2 level 10-15 times higher during the Little Ice Age? No men and no warming. Go tho the link I left above for some good info.