I came across an interesting story. A different perspective that brings together the mystery of the mega-fauna die-out in the last ice age, science-geek level photosynthesis details, global warming / climate change, crop science, and more. It was written sort of like a mystery story, but I think it merits consideration and more research.
The title of it is The Solution to Ice Age extinctions. The title is a joke, or at least a play on words and meaning, at a couple of level.
Ultra-short version: there is more than one type of photosynthesis, they operate at different efficiencies at different CO2 concentrations, different types of plants utilize different methods of photosynthesis, and different animals eat different types of plants. Nothing earth-shattering from each of these items individually. Very interesting when considered together, because organisms respond to changes in the environment.