"On its current trajectory," Craig Martin & Scott Moore write at Foreign Affairs, "the world is unlikely to meet the limits it set for itself in the 2015 Paris Agreement to halt global warming. ... As this reality sets in, once fringe ideas about how to artificially cool the planet are gaining traction. One such idea is lowering global temperatures by effectively shading the planet, a process known as solar geoengineering."
The premise of solar geoengineering is simple: If we reduce the amount of sunlight (and accompanying heat) that reaches the surface of the planet, we get lower temperatures.
The devil isn't just in the details --- do we seed the upper atmosphere with sulfates, spray seawater into clouds to lighten their color and make them reflect sunlight, maybe even park a gigantic Mylar (TM) mirror in orbit? --- but in the fact that cooling the planet portends negative as well as positive consequences. Lower crop yields in some agricultural zones, for example. More violent/damaging weather in certain areas, too. Good things we can maybe predict, bad things we can't necessarily foresee.
That makes the whole idea a political problem that, Martin and Moore write, "will require a new multilateral treaty with the primary purpose of prohibiting unauthorized deployment and establishing a collective decision-making process for approving and governing any potential future use."
Count on a long wait and a great deal of acrimony before something, anything, might actually happen ... unless rogue state or non-state actors take matters into their own hands. For a gripping fictional account of what that might look like, read Neal Stephenson's Termination Shock. You'll learn a lot, and enjoy the learning.
Let's look at this from four highly debatable, but not implausible, premises:
First, the earth is warming, at least partly due to human action.
Second, the warming represents something at least approaching an existential crisis for humanity, making life --- on balance --- worse for humanity and maybe, MAYBE even portending our eventual extinction.
Third, most of humanity is NOT going to abandon the Industrial Revolution and its consequences --- healthier, longer, more prosperous lives --- to stop the warming.
Fourth, the that Revolution isn't moving fast enough to get us to "net zero emissions" (with the supposed benefit of ending the warming) in a timely manner.
If those four things are true --- and, like I said, they are all debatable --- then the alternative seems to be "do some solar geoengineering" or "get used to living in an oven that's still pre-heating with no top in sight." The nature of politics probably sticks us with the latter.
As a libertarian, I'd naturally like to see matters resolved with minimal if any government involvement ... but figuring out what level of "pollution" constitutes an actionable tort or how to penalize those whose externalities warm up my house in ways that modify their behavior, may prove even more complicated than "a new multilateral treaty with the primary purpose of prohibiting unauthorized deployment and establishing a collective decision-making process for approving and governing any potential future use."