A new report in the journal Science by an international panel of scientists warns that in the next 50 years, crop yields of various staple crops, including wheat, are expected to decline by 20 - 30 percent across the entire tropical and sub tropical zones of the planet - home to half of humanity. This is due to mean average growing season temperatures rising above 86 degrees Fahrenheit, a kind of upper limit for many crops. During the same time period, world population is expected to grow to somewhere over 9 billion. The group is "urging world leaders to dramatically alter their notions about sustainable agriculture to prevent a major starvation catastrophe by the end of this century among the more than 3 billion people who live relatively close to the equator."
"I grow increasingly concerned that we have not yet understood what it will take to feed a growing population on a warming planet," said Federoff (science and technology advisor to Hilary Clinton), who also is a biology professor at Pennsylvania State University.
The challenge is becoming more difficult, the scientists said, because the world's population is likely to have increased more than 30 percent, to 9 billion people, by 2050.
Even without climate change, feeding all of these people will require doubling the grain production in the tropics, Battisti said, but a warmer climate will reduce yields because the temperature will be too high to achieve the most efficient photosynthesis. That factor, combined with less rainfall in major food-producing regions and increasing pressure from pests and pathogens, is likely to cut major food crop yields a minimum of 20 percent to 30 percent.
Battisti noted that the so-called green revolution in agriculture produced a 2 percent increase in yields per year for 20 years, primarily through development of new grain varieties and use of fertilizer and irrigation. But there is little, if any, new land available for farming, and such yield increases cannot be sustained without further innovation. In addition, there already are 1 billion people, mostly in the tropics, who do not have enough food for a healthy life.
"We're really asking for yield gains comparable to those at the peak of the green revolution, but sustained for an unprecedented length of time, 40 years, and at a time when climate change is acting against us," he said.
By combining direct observations with data from 23 global climate models that contributed to Nobel prize-winning research in 2007, Battisti and Naylor determined there is greater than a 90 percent probability that by 2100 the lowest growing-season temperatures in the tropics and subtropics will be higher than any temperatures recorded there to date.
They used the data as a filter to view historic instances of severe food insecurity, and concluded such instances are likely to become more commonplace. Those include severe episodes in France in 2003 and the Ukraine in 1972. In the case of the Ukraine, a near-record heat wave reduced wheat yields and contributed to disruptions in the global cereal market that lasted two years. "I think what startled me the most is that when we looked at our historic examples there were ways to address the problem within a given year. People could always turn somewhere else to find food," Naylor said. "But in the future there's not going to be any place to turn unless we rethink our food supplies."