I don't know, I've grown quite sceptical about what technology can achieve against this problem. I'm pretty sure increasing food spending to 25% of GDP would involve a massive societal shift. Whatever way you look at it we are in for a lot of pain.

And yes, it is a big shift with lots of pain. A massive increase in food prices would be required, which would result in riots across the third world.

Easier and cheaper to spend a trillion or five to halt the increase in carbon emissions.

Rather than trying to save the current system with dystopian technologies, the ideal would be to give it up and start moving to a new one, preferably in an organized manner (e.g. Starting with the Green New Deal), instead of waiting for an otherwise inevitable revolution.

It did remind me of an off-topic pet peeve - it's absurd to start thinking of a colony on Mars before colonizing the Sahara and the Antarctic, both being orders of magnitude easier and more useful than a colony on Mars.

Unfortunately, there is no way to still have industrial Capitalism, even under a global Green New Deal, and reduce emissions enough for the world to not go through catastrophic global warming. If we do nothing, the transition will be catastrophic as you mention. If we try to start major reforms today, we might have a somewhat smooth transition. But there is no way to avoid the transition to something new.