Thing is, the expected consequences of global warming are very much not uniform. Some regions will become much less habitable, but others will have their agricultural capacity increased. So it really matters which 20%-30% of the populace will be affected and how that relates to the global power balance.

Many of the currently wealthy regions could still say "why would you want colder winters?" because they can still breathe in summer (and would not want colder summers) and the locales becoming uninhabitable are somewhere else inhabited by someone else they don't care about.