A few things here. I think as a whole society has lost the ability (not sure how much there was before, but now it is definitely less) to discuss nuance. The example you mentioned is pretty bad to make your point though, as the 12 year discussion has far more nuance at least in academia and left-leaning areas than on the right wing.
Just to make sure we are on the same page, the 12 year deadline was part of an IPCC special report and it was not referring to the demise of the human species, but it was referring to the limiting global warming to 1.5 C which was a seen as a critical factor.
In the report we will find quotes such as
This is what is part of the discussion in academia and policy and you will note that not even very left leaning governments at any point mentioned death within a decade. I am actually not sure where your claim of a 12 year death deadline came from, but it really sounds like distortion from right wing pundits. Even in left-
I am not saying that the left is free from those mistakes, but the example you picked out does not really help your point.
But to get back to my earlier point, it is true that outside (and sometimes also within) academia these things are almost never discussed with the necessary detail , and it is quite obvious why. Folks do not want to think. I get that, though in the past there was at least some level of perceived accountability with regard to falsehoods. But also folks were not as easily distracted by social media.
We also see it with things which have immediate impact or are just simple facts (Sandy Hook shootings, COVID-19 pandemic) where folks increasingly just design their own reality. Of course this changes the whole discourse as we now have a whole generation of kids growing up with cell phones and social media, and many of those will be in the positions were said nuance would have been important. Yet modern politics demonstrated that facts don't matter, so why shouldn't they choose the easier road?