and how does more CO2 make this worse? Say a country like Sri Lanka has 1 million tons of rice per year - that contain 100 tons of minerals. After the CO2 enrichment they get 1.2million tons of rice, but with they contain still 100 tons of minerals.

Things Sri Lanka can do:

1. eat more rice, all 1.2 mil tons of it, for the same amount of minerals (this would lead to obesity).

2. plant and eat 1 million tons of rice per year, leaving empty 1/6 of the previous fields free for other use. In those 1/6 of the fields, they can now grow carrots and mushrooms and lentils and other highly nutritious stuff. It might even leave them with extra land for football fields.

How is this an issue? I swear: sometimes people want to find a negative even in the most positive outcomes.