My answer to a Quora question...

The great nutrient collapse
Dave Burton
Dave Burton, IPCC AR5 WGI expert reviewer

No. That "Great Nutrient Collapse" Politico story is propaganda, not science.

The studies have not found evidence that the overall nutritional value of crops is reduced by the improved plant productivity from CO2 fertilization. Rather, they've found that when crops are grown in iron-poor or zinc-poor soil, the larger yields may contain lower levels (though not lower overall quantities!) of those micro-nutrients.

As it happens, dietary shortages of those micro-nutrients are easily resolved through either fertilization or very inexpensive nutritional supplementation. In the case of iron, it can be as simple as cooking in cast-iron pots.

It is possible to contrive growing conditions in which something other than CO2 limits plant growth and health, or in which a shortage of some soil nutrient causes better crop yields to be accompanied by reduced levels of some nutrient, but such contrived conditions are easily avoided through normal agricultural fertilization practices. Under real-world conditions, additional CO2 is dramatically beneficial for agriculture, to levels far beyond what we can ever hope to reach in the outdoor atmosphere, and the nutrient value of crops grown with extra CO2 is not significantly different from other crops.

If you want proof of that fact, read up on the relative nutritional values of crops grown in greenhouses vs crops grown outdoors.

Most commercial greenhouses use CO2 generators to keep CO2 at 3x to 4x ambient levels, at significant expense. That's an increase 6 to 10 times as great as the measly ~125 ppmv increase which mankind's fossil fuel use has caused in outdoor levels. Greenhouse operators spend the money to keep CO2 levels that high because doing so dramatically improves the growth of most plants. If the modest increase in outdoor CO2 levels were making crops significantly less nutritious, then crops grown in greenhouses at dramatically higher CO2 levels would necessarily be dramatically less nutritious than crops grown outdoors.

But, of course, that is not the case. Studies show that food grown in greenhouses at elevated CO2 levels has about the same nutritional value as food grown in open fields at ambient CO2 levels.

Dave Burton