Arctic is warmest it's been in 10,000 years

[Labster]

Wars do have a tendency to cool the Earth by blowing things up. You can see a noticeable dip in global temperature in the 1940s, but it's hard to say it wasn't just a natural local minimum either. Particulate matter pollution has the main problem that it, um, kills people. Millions so far. And you don't want your PM to land and turn into black carbon on snow, either. But yes, some of the geoengineering proposals involve injecting particulates into the stratosphere to provide a solar shade.

Launching an orbital solar shade is one approach. Spaceflight is getting a lot cheaper, to the extent that next year Chengdu is purportedly going to launch an artificial moon for night lighting. Increasing insolation with a reflector is kind of backwards, unless you can get equivalent energy savings out the other end. Either way this sort of solar shade is a good deal safer than the particulate approach, as turning it off is a simple as rotating the craft.

Either that or seeding jet fuel to promote high altitude contrail formation. Less light to the surface - less heat.

Haha nope. High clouds warm the surface, low clouds cool the surface. Contrails provide a global average +0.012 W/m² radiative forcing, with the bulk from night and winter flights. You do not want this to increase. Cloud seeding/silver iodide in general is a tricky thing, because it can theoretically work, but it's impossible to prove that it did. And if you could prove that it worked, then someone downwind could sue you for stealing their rainfall. I got the feeling from my professors that cloud seeding was all the rage for a while and then they collectively decided there was probably nothing there and moved on.

Actually aerosol and cloud physics and how it feeds back into albedo is massively complicated. Actually the wikipedia page on albedo has a really good overview.