You also don't need an international agreement to impose tariffs on any country that emits more than a given amount of CO2 per capita, and if more than a couple of countries impose those conditions (or even just one big one like the US) then it gives others domestic cover to do something meaningful because they can argue they have to do it to avoid the tariffs. Meanwhile they can "retaliate" by imposing the same conditions and soon enough everyone is hitting their targets to avoid all the tariffs, without anyone ever having to sign up for a unified agreement.

I want it to work. I'm just not sure it is, or if humans are even capable of coordinating on the scale required to address this problem outside of some geoengineering solution.

Just like we aren't capable of operating without corruption or war because a certain group of people won't "get out of the way"

The same way countless other endangered subsets of humanity (particularly those facing essentially total annihilation by, or permanent subservience to a foreign occupier) have: by recognizing the simple the simple fact that they'll either have to put their heads together, put aside their differences, and "figure out a way" to prevail against overwhelming odds --

or face the inevitable consequences of failing to do so.

No, the only way anything changes is at the point of a spear. There has to be an imminent and tangible threat, now. Otherwise, it’s business as usual.

Anyway, Civilizations come and go. The Romans, at one point, had running water too

Whose to say we ain’t bout to run into another dark age?

But for sure, Silicon Valley has nothing to contribute

There’s not a single drop of revolutionary blood in that city