Interestingly, while CO2 may spur the growth of certain plants, it can also reduce the nutritional value of certain agriculturally important food crops:
"The nutritional value of agriculturally important food crops, such as wheat and rice, will decrease as rising levels of atmospheric carbon dioxide continue to reduce the concentrations of protein and essential minerals in most plant species [Very Likely, High Confidence]."
It is also likely to increase pests (such as weeds and insects) which will result in competitive effects within agriculture and an increase in pesticide use:
" Rising carbon dioxide concentrations and climate change will alter incidence and distribution of pests, parasites, and microbes [Very Likely, High Confidence], leading to increases in the use of pesticides and veterinary drugs [Likely, Medium Confidence]."
https://s3.amazonaws.com/climatehealth2016/high/ClimateHealth2016_07_Food.pdf
