There’s levels of societal collapse, mass migration can destroy the existing social fabric without necessarily being that terrible. Fertility rates being so low means developed countries will likely want large numbers of immigrants.

At the other end stopping all CO2 production tomorrow would result in severe consequences. We can’t transport food to cities without burning fossil fuels. Obviously that doesn’t mean every current use case is worthwhile, but we can’t ignore the short term here.

The good news is we’re actually making a lot of progress on climate change. The electric grid being ~90% very low carbon emissions by 2050 is a realistic goal and would avoid the worst predictions.