Let's just discuss global warming for a bit. The science itself is pretty well settled at this point. The earth is indeed warming and human activities are the culprit. CO2 levels in the atmosphere are higher today than they have been in likely millions of years and do act in a greenhouse fashion. The recent increase is strongly correlated with the onset of the industrial revolution and the explosion of the human population. None of this is realistically in doubt.
Although this has been generally known for decades, the global will to do anything to counteract the trend of global warming has been, basically, a dismal failure. The Kyoto protocol, so celebrated in its time (back in the 1990s), was, with all its faults, a wonder of international diplomacy. Yet there were major national polluters who never adopted it at all and others who never acted within its principles in a serious fashion. And the reason for this is obvious. In a competitive world, to ask the nations of the world to voluntarily gear down on their economic engines, is wasted breath at best. Indeed, knowing a little bit about human behavior, it should be obvious that just asking the world to try to cut down on its energy use, is a strategy of minimal efficacy.
To my mind, it kind of like asking a severe diabetic to, y'know, try to cut down on the sweets. That strategy might work on a minority of well-motivated patients, but will far and large be an abject failure. Global warming is just like many modern human diseases - they are problems stemming from human behavior. Granted, they could be fixed by simply changing people's behavior, but that just ain't going to happen. I think that continuing to harp on trying to reduce carbon emissions are well intentioned, but just are not going to cut it. The world's appetite will not slake and the CO2 will continue to rise.
So, why aren't we trying other things? There are plenty of drugs that exist which treat and control diabetes, heck there are even surgeries which may even offer a cure. Sure, most type-2 diabetes is caused by human behavior, but so what? We can treat it by intervening in other ways. Can the same be said about global warming?
Yes! The issue is not that humans are releasing too much CO2 into the atmosphere. The issue is that it stays there and causing too much warming. But there are things we can actively do which can pull CO2 out of the atmosphere and put it in safe places. This is little different from pulling sugar out of the bloodstream and putting it back into cells where it's safe. For one, a major carbon sink are the world's forests. When trees grow they grab carbon from the air and use it to grow. Granted, stopping active deforestation is the simplest and cheapest way to maintain this carbon sink, but the world could also be actively reforesting millions of acres of unused flatlands. It's so simple, but adding millions of trees to our world would be awesome for our ecology, biodiversity and would suck in billions of tons of CO2 from our atmosphere. Why is this not already being done?
Iron is an excellent fertilizer for ocean algae. With carefully selected ocean sites, we could be dropping tons of cheap iron particles which would create huge algae blooms with loads of carbon dioxide stuck within it. The algae would eventually die and then sink to the ocean floor, taking all of that carbon down with it. This literal carbon sink could keep the carbon safely out of the atmosphere for millennia. There are numerous other hypothesized mechanisms to trap carbon out of our atmosphere. Some are higher tech and may cost more, but are still worth considering. I don't need to list all of them here. If you are truly interested, the internet is available to all for perusal.
Now, managing the carbon is just one side of the equation. The other major variable is simply the heat itself. Even if atmospheric carbon levels remained unchanged, is there something we can do that would cool the Earth? Of course! What killed the dinosaurs? Global climate change set off by a meteorite which on impact released huge amounts of dust into the atmosphere which blocked the Sun's rays and cooled the Earth. It's also been shown that the release of sulfate compounds from volcanic eruptions cause climatic cooling effects. Could this be done artificially? Sure. There have even been more imaginative proposals to modify sunlight by placing mirrors or lenses in orbit.
The bottom line is that global warming is happening. The best solution would be to cut down on our emissions, but that just ain't gonna happen - and even if it did, it's probably too late. The next best thing is to make some alternative interventions. Like in medicine, there may be side effects, but I'd rather brave those than to just allowing global warming to happen.
[Plus, keep an eye on this venture. It's the most reasonable engineered mechanism for fusion power that I have yet to see.]