I was surprised to find that an article on the dry topic of crop yields was surprisingly compelling. It seems to have it all: new information pulled together from a collection of studies that suggests the current consensus was based on an outdated technique. The topic is politically charged, and the editors even let the authors get away with a pun in the title ("Food for Thought"). How does this all fit together?
As atmospheric carbon levels go up and the planet warms up, crops are expected to be impacted in a variety of ways. Increased temperature and CO2 are expected to accelerate growth, but soil moisture will decrease, potentially counteracting these effects. Based on a number of studies, it was expected that these factors would largely balance out, with a slight decrease in crop yield possible. The new study addresses one of these factors: how CO2 affects growth and yield of crops. The authors note that the estimates of these effects being used in assessing the impact of rising carbon levels are based on experiments in enclosed buildings, where it's easy to control the atmosphere. But technology has since improved, and free-air concentration enrichment (FACE) technology allows crops to be grown in the open under controlled atmospheric conditions, more closely approximating real-world conditions.
What happens when you compare the results of FACE experiments with enclosed results? The enclosed experiments produce crop yields that are more than two-fold higher than those produced using FACE technology. This, in turn, suggests that the expectations for the future crop yields may be over-estimates. As the authors note, "This casts serious doubt on projections that rising CO2 will fully offset losses due to climate change." They do, however, wrap up on an optimistic note: crop plants have been selectively bred for a number of properties, and increased growth at higher CO2 levels may be as accessible to breeding as anything else. The same technology that allowed us to recognize the problem may be useful in breeding a correction for it.