> since higher CO2 means plants can keep their stomata closed more [e.g. 5]

And that apparent silver lining's actually got a downside, too. Plants working hard to draw up water is a Good Thing, because that water is the only source of nitrogen and other elements needed to make proteins and vitamins.

CO2 just gets turned into carbs; it makes plants grow big and tall but less nutritious. This won't be a problem for us overfed gluttons in the West, but it is going to exacerbate malnutrition issues in poorer regions of the world.

See e.g.:

https://www.nature.com/scitable/knowledge/library/effects-of...

http://advances.sciencemag.org/content/4/5/eaaq1012