A parallel between the demographic crisis and global warming is that for each, one side of the partisan divide largely doesn’t think it’s a problem at all. And for each side, the deniers are straight up wrong. Human caused global warming is essentially a fact. Declining demographics and the problems it causes are simply true. Being in denial of either of these is not a difference of opinion, but being wrong about the ample and sufficient evidence. Disagreeing about what to do about these problems once they are recognized is legitimate and complicated, so is disagreeing about some of the consequences, but, denying them as problems is going against reality.
Unfortunately, global warming has been coded as a liberal issue. The demographic crisis has been coded as a conservative issue. But neither of them them should have partisan or ideological coding. They are both real problems that are happening. The only disagreement should be what to do about these problems, not whether they are severe problems with difficult consequences, because that is in the realm of fact.