Futurama posits two possibilities (maybe more)
1: Harvesting enormous ice cubes from other planets and dropping them into the Earth’s ocean’s
2: Moving the Earth farther away from the Sun
Push all of the continents back to where they had started.
One Continent to rule them all, One Continent to find them, One Continent to bring them all, and in the darkness bind them.
PANGEA FOREVER
Maybe we could use our technology for more Earth-based solutions. There may be a link between the Little Ice Age and increased volcanism, with the former possibly being tied to increased sulfuric acid providing effective, temporary reflectivity…
Throughout the Little Ice Age, the world experienced heightened volcanic activity. When a volcano erupts, its ash reaches high into the atmosphere and can spread to cover the whole earth. The ash cloud blocks out some of the incoming solar radiation, leading to worldwide cooling that can last up to two years after an eruption. Also emitted by eruptions is sulfur, in the form of sulfur dioxide gas. When it reaches the stratosphere, it turns into sulfuric acid particles, which reflect the sun’s rays, further reducing the amount of radiation reaching Earth’s surface.
Maybe we can outfit airliners with sulfuric acid distributors? Granted, injecting clouds of sulfuric acid into the stratosphere artificially probably offers more risk than reward (Acid Rain). But, hey, the OP asked how hard it would be, not if it would be a good idea and if there would be no unintended consequences.
That’s roughly a surface area the size of Mongolia.
There’s one of these in every crowd. And the answer is that it isn’t the equilibrium end-state that’s necessarily the problem, it’s the climatic and ecological stresses created by rapid change, as well as permanent changes in local climate regimes, global sea level, and acidification of the oceans. It’s an ironic comment to make considering we’ve just been through a week of some of the most extreme weather on record in the US and around the world. According to the UN, in the past 20 years weather disasters killed 606,000 people, left 4.1 billion injured, homeless or in need of aid, and accounted for 90 per cent of all disasters.
Of course it usually isn’t possible to link a particular weather event to climate change, but observations bear out the model predictions: extreme weather is occurring more frequently. The rate of extreme weather events in the past decade is twice what it was 20 years ago. I provided some cites in a previous discussion here on the link between climate change and extreme weather, and the potential impacts on insurance costs and global security.
Regarding the OP, I think the two words “unintended consequences” already mentioned sum it up perfectly. It would be tragically ironic if, after screwing up the climate for the next couple of thousand years, we screwed it up even more by trying to “fix” it in some artificial ham-handed way because we couldn’t bring ourselves to actually cut GHG emissions. As mentioned, injecting sulphate aerosols into the atmosphere would defer the problem for a short time, and in return we’d be killing all our lakes and rivers and our buildings would be dissolving in acid rain. That’s just one example. Many of the others are worse.