The global solutions will eventually happen. Right now nationalism gets in the way of it, but on the timescales of geology, nationalism is a blip. Hell, many scholars cite 1648 as the creation of the current system – en.wikipedia.org/wiki/Westphalian_system – so hopefully this is just a phase and we’ll get over it and start global scale geoengineering before we get cooked :)
Can you imagine a UN agency in charge of sun shades positioned at Sun-Earth L1 that reduced the total sunlight hitting the earth by 0.1% and halted the heating problem entirely? Wouldn’t solve the carbon dioxide levels, but it’d be a start :D
(The orbital mechanics folks can chime in here. Sunshades at L1 are unstable because L1 is unstable, and sunlight exerts pressure on them like solar sails. However, there are quasi-stable positions slightly sunward of L1 where you can balance these instabilities and actually use the solar sail effect for station keeping in a swarm. It would require launching a lot of rockets, but is entirely doable with today’s technology. Said rockets use hydrocarbons to launch, ironically.)