The Great Nutrient Collapse:

When the researchers shined more light on the algae, the algae grew faster, and the [zooplankton] had lots and lots to eat--but at a certain point they started struggling to survive. This was a paradox. More food should lead to more growth. How could more algae be a problem?

...The biologists had an idea of what was going on: The increased light was making the algae grow faster, but they ended up containing fewer of the nutrients the zooplankton needed to thrive. By speeding up their growth, the researchers had essentially turned the algae into junk food.

...it's been understood for some time that many of our most important foods have been getting less nutritious. Measurements of fruits and vegetables show that their minerals, vitamin and protein content has measurably dropped over the past 50 to 70 years. Researchers have generally assumed the reason is fairly straightforward: We've been breeding and choosing crops for higher yields, rather than nutrition, and higher-yielding crops--whether broccoli, tomatoes, or wheat--tend to be less nutrient-packed.

In 2004, a landmark study of fruits and vegetables found that everything from protein to calcium, iron and vitamin C had declined significantly across most garden crops since 1950. The researchers concluded this could mostly be explained by the varieties we were choosing to grow.

Loladze and a handful of other scientists have come to suspect that's not the whole story and that the atmosphere itself may be changing the food we eat. Plants need carbon dioxide to live the same way humans need oxygen. And in the increasingly polarized debate about climate science, one thing that isn't up for debate is that the level of CO2 in the atmosphere is rising.

...as the zooplankton experiment showed, greater volume and better quality might not go hand-in-hand. In fact, they might be inversely linked. As best scientists can tell, this is what happens: Rising CO2 revs up photosynthesis, the process that helps plants transform sunlight to food. This makes plants grow, but it also leads them to pack in more carbohydrates like glucose at the expense of other nutrients that we depend on, like protein, iron and zinc.