Because actually, the biggest change came on May 9th, 2013…
If I recall my understanding correctly, it’s 1) because there hasn’t been consistently this much CO2 in the atmosphere since an era when the planet whose climate was fundamentally different and 2) that this is an escape velocity type thing, where it becomes harder and harder for us to get back under 400ppm CO2 in the atmosphere, because of how long it takes for CO2 to be absorbed. Thus, climate change will spin out of control far faster in this new, different environment.
So literally, yes, we were climate changing, but post 2013 things are indeed a lot more grim and the outlook less clear.
These people are fools who are making a conscious choice to ingest information that would challenge their worldview.
Starve the Beast. The conservatives use it for everything. Run on government not working, and then working to dismantle government to prove it.