Asklemmy

Well... Earth becoming more like Venus is an inevitability in the high hundreds of millions of years (and for scale, multicellular life has been around for roughly 5-600M years, with the more than 3 billion before that just being simple single-celled prokaryotic life), but that is completely independent of anthropogenic climate change, it is because of the expansion of the sun towards it's red giant phase. In terms of being habitable to life, Earth is easily past the half-way mark already, no matter what. However, that is far enough out that it doesn't bear worrying about and isn't something we can have any sort of impact on.

That said, the climate change that we as a species are causing right now could lead to a runaway greenhouse effect on much shorter time scales. The fact is, there have been times in Earth's history where it has been so hot that complex life could mostly only survive at the poles (with the equator being a death zone to all but simple, single-cellular extremophiles) and there have been times where Earth was encased almost entirely in ice except perhaps at the equators - not just our usual conception of an ice age, but "snowball earth," and this was likely caused by certain forms of simple life, fascinatingly enough. The feedback loops we are triggering right now have a potential to drastically change the composition of the atmosphere on a far shorter timescale, one in which we are talking about an end to most complex life (obviously ourselves included). It was almost certainly volcanism that caused Venus to go from a mostly habitable planet to the completely, utterly inhospitable world it is. Volcanism has also been responsible for extreme heat and mass extinctions on Earth, but obviously it never tipped over into Venus-like territory. The thing is, right now we're changing the atmosphere at a rate far faster than volcanism has in the past! And rate of change matters a lot with this kind of thing. I'm repeating myself, but again, it is not a certainty but it is a possibility that anthropogenic climate change could hit tipping points that Venus-ifies Earth on a much shorter, nearer term than anything relating to the expansion of the sun, on time scales that are worth worrying about (if we value humanity as a whole), and is the sort of thing we can have an impact on.