CO₂ is a fertilizer for plants because plants use sunlight, water, and CO₂ to synthesize the glucose they need to grow (a process called "photosynthesis"). Since increased atmospheric CO₂ accelerates plant growth, commercial greenhouses artificially raise CO₂ to what it would be under gloomy global warming scenarios. Thus many see accelerated plant growth as a silver lining to the greenhouse effect.

But as described in the Nature article "The Other Greenhouse Effect", this silver lining may be insidiously tarnished. There isn't a lot of research into the effects of CO₂ on plant nutrition, but the studies that exist suggest a variety of negative effects. Researchers have observed significantly lowered protein levels (especially wheat gluten, which reduces baking quality), lowered trace mineral content, lowered Vitamin C in potatoes, and lowered calcium in soya beans (problematic since soya beans are used to make dairy substitutes).

There is even evidence that plant yields in the real world of global warming will not be higher, since other factors such as higher temperatures and drought will negate the effect of increased CO₂.

Humans aren't the only ones to eat plants, as Lisa points out in her post. Grazing livestock also eat plants, and we eat the livestock. So the full range of what we eat is affected.

Other parts of the food chain are also impacted. One of the studies cited in the Nature article found that certain types of plant pests thrive on the altered soya bean leaves, laying eggs that destroy the following year's crop.

Moral: It's not nice to fool Mother Nature!