[ben_w]

And also a poison for them — just as oxygen is both of those things for us. (If oxygen isn't even a metaphorical food for us, then neither is CO2 for plants).

Unfortunately, "food" is more complex than "how much carbohydrates do you get per day?"

[coffeebeqn]

We still have ways to go to that. From the current 400 ppm to about 2000ppm before the apocalypse. Until then the yields will generally improve from today’s baseline. There might be other systems that break before that and we get plantocalypse earlier