What comes after 2100?

I was fascinated to learn in The Unhabitable Earth by David Wallace-Wells that climate models end in 2100 as a matter of convention. I’d be interested to learn about how this convention emerges and what effect it has had on climate science. It’s easy to see the epistemological reasons for this, as the conditions being modelled become sufficiently complex that forecasting past a certain point becomes close to untenable. But why choose the turn of the century? It’s such a resonant point at which to cut off. I find it unnerving because, for example, my niece and nephew (5 and 3 respectively) could be expected to have an excellent chance of living to see the next century. A generation are being born now who will live to see past this horizon, with their children living to confront what could possibly come to be a literally uninhabitable earth.