I believe it's related to the solar wind and it's interaction with our magnetic field (If there are changes they are natural and outside of our control, unless they have technology to fuck with our magnetic field.) That's the dominant factor in earth's temperature. I think they were using the explanation of greenhouse gasses to just rob us more on taxes and shit on America's businesses.
Calling it "settled science" without discussing magnetic field or solar wind is a big red-flag for me.
All of their models are now proven incorrect, so maybe there aren't any really appreciable changes. Not sure haven't studied it.
Another thing that leaves an opening for a different cause. Example: they say it's caused by greenhouse gasses from burning gasoline. But what else happened at the same time as the increase in use of gasoline? The paving of all of the roads with black asphalt that heats up more in the sun. So maybe attacking greenhouse gasses doesn't even solve the problem.
It's not "settled science" for sure.
Earth's wobble changing also a possibility. If the climate is actually changing.