On a side note, can you imagine the United Nations agreeing to a planetary geoengineering plan? I can't.
Yes I can, actually. And they will. The question is, how many billions of people are going to die before this happens. Climate change is occurring, this is a hard fact. Most times in nature, change doesn't precipitate gradual linear effects, but rather a tipping point where things happen very rapidly. Sooner or later, we are going to cross an environmental tipping point, and you will see some sudden massive flooding or crop failure and a lot of people will die.Hopefully, not too many, but I suspect that it is going to be a lot. You might even see some wars of extermination fought over critical resources, such as potable water supplies.
The simple fact is, people cannot continue their current behavior. The way you live with a planetary population of 1 billion isn't the same when you have a planetary population of 10 billion. Either we will come to some global consensus about how we will fix this problem, or vast numbers of people will die and the population will be reduced to the point where change isn't needed. Nature will 'find its level' in any event.