I don’t think human psychology will allow a united approach to global warming. Too man people are too stupid, to egoistic or just in such a tight spot they can not afford being “climate-friendly”.
So I wonder if there are Mega-Projects available to stop global warming?
Some coming to mind:
Reflector mirror at Lagrange1 between Sun and Earth - even a 1.000.000km² mirror from ultrathin film would weigh 1000 tonnes at most.
Giant Air Scrubers and I mean giant. They would dwarf the pyramids and remove pullutants and CO² from the athmosphere.
In addition I think a originator principle should become common: Any nation not really trying to act clean should simply be burdened with massive tariff measures. Using modern technology it shouldn’t be too hard to find nations who polute the ocean unnececerrally.
Edit, it became reality:
Except that has already failed. We already have sent enough CO₂ into the atmosphere that global warming is already here. You can no longer solve the problem by just stopping greenhouse gas emissions. All serious solutions now involve some form of geoengineering. Either block out the sun or pull CO₂ out of the air, those are the only possible options.