Could global warming's top culprit help crops?

Many scientists fear that global warming will hit staple food crops hard, with heat stress, extreme weather events and water shortages. On the other hand, higher levels of carbon dioxide—the main cause of ongoing warming—is known to boost many plants' productivity, and reduce their use of water. So, if we keep pouring more CO2 into the air, will crops fail, or benefit? A new study tries to disentangle this complex question. It suggests that while greater warmth will reduce yields of