They are doing that one abit more subtly. They can't challenge it directly, as that combats their opinions of themselves as 'scientific' but I am seeing papers coming out of Midwestern ecology schools (which are subsequently pushed hard on social media), that are pushing forward a hypothesis that 'we just don't know enough about the carbon cycle, there are lots of unaccounted carbon creating beings that could be helping with the warming', as well as people saying that because there have been no apocalyptic universal Hollywood spectacal collapse that 'the climate scientists got all their predictions wrong'.
It'll creep into mainstream thought over time, especially as it becomes too late to change.