Maybe they forgot a keyword? It certainly isn't the sole cause of global warming/climate change, but it is real.

CO2 in the atmosphere--what's historically known as the greenhouse effect--leads to earth's warming. CO2 emissions are also undeniably connected to the the greenhouse effect, which we clearly have a role to play in. That's science that no one disputes.

But somehow people come out of the woodwork as climate change denialists.

It doesn't really make sense unless seen through a political lens, since politics is antithetical to science in a lot of ways.