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  Why Global Warming Portends a Food Crisis

  It can be difficult in the middle of winter — especially if you live in the frigid Northeastern United States, like I do — to remain convinced that global warming will be such a bad thing. Beyond the fact that people prefer the warmth to the cold, there's a reason the world's population is clustered in the tropics and sub-tropics: warmer climates usually mean longer and richer growing seasons. So it's easy to imagine that on a warmer globe, the damage inflicted by more frequent and severe heat waves might be balanced by the agricultural benefits of warmer temperatures.

  A comforting thought, except for one thing: it's not true. A study published in the Jan. 9 issue of Science shows that far from compensating for the other damages associated with climate change (heavier and more frequent storms, increasing desertification, sea level rise), hotter temperatures will seriously diminish the world's ability to feed itself. David Battisti, an atmospheric scientist at the University of Washington, and Rosamond Naylor, director of the Program for Food Security and the Environment at Stanford University, analyzed data from 23 different climate models and found a more than 90% chance that by the end of the century, average growing season temperatures would be hotter than the most extreme levels recorded in the past.

  That means that barring a swift and sudden reduction in greenhouse gas emissions, by the end of the century an average July day will almost certainly be hotter than the hottest heat waves we experience now. And the extreme heat will wilt our crops. Battisti and Naylor looked at the effect that major heat waves had on agriculture in the past — like the ruthless heat in Western Europe during the summer of 2003 — and found that crop yields had suffered deeply. In Italy maize yields fell by 36% in 2003, compared with the previous year, and in France they fell by 30%. Similar impacts were seen during a major heat wave in 1972, which decimated farmers in the former Soviet Union, helping to push grain prices to worryingly high levels. If those trends hold in the future, the researchers estimate that half the world's population could face a climate-induced food crisis by 2100. "I'm very concerned," says Naylor. "How are we going to feed a world of eight or nine billion, with the effects of climate change?"

  It's true that as temperatures warm, there is likely to be a temporary, beneficial effect on agriculture. (Like people, plants generally prefer the warmth to the cold, and they may flourish with rising levels of CO2.) But as research from Wolfram Schlenker at Columbia University shows, as average temperatures continue to warm, those benefits dwindle and then eventually reverse, and crop yields begin to decline. "It simply becomes too hot for the growing plants," says Naylor. "The heat damages the crops' ability to produce enough yield."

  What's more, Battisti and Naylor are looking only at the impact of higher temperatures in their study — not at the possible impact of changing precipitation patterns. Yet many climatologists believe that global warming will make dry areas drier and further damage farming, which is especially dire news for sub-Saharan Africa, a region that already struggles with heat waves, droughts and famines, even as population continues to grow. "Climate change is going to be a major concern for Africa," says Nteranya Sanginga, the director of the Tropical Soil Biology and Fertility Institute of the International Center for Tropical Agriculture, in Nairobi. "We could lose whole growing seasons."

  With these frightening predictions in mind, we need to try to heat-proof our agriculture. That can be accomplished by using crops that have proven resistant to extreme heat — like sorghum or millet — to breed hybrid crop varieties that are more capable of withstanding higher temperatures. We'll need to drop any squeamishness about consuming genetically modified crops — unless we can tap the power of genetics, we'll never feed ourselves in a warmer world. But we'll need to act quickly — it can take years to breed more heat-resistant species, and investment in agricultural research has shriveled in recent years.

  We also need to focus on improving the agricultural productivity of those parts of the world that have been left behind by the Green Revolution — such as Africa, where average crop yields per acre remain well below those in Asia or the West. One simple way is to increase the amount of fertilizer available to African farmers. Sanginga notes that about 440 lbs. (200 kg) of nitrogen fertilizer is generally needed to grow five tons (5,000 kg) of maize, but the average African farmer can afford only 8 lbs. of fertilizer. We can also work on safeguarding the degraded soils of Africa, where almost 55% of the land is unsuitable for any kind of cultivated agriculture. Help is on the way: the African Soil Information Service is launching a real-time, digital map of sub-Saharan Africa's soils, which should allow farmers and policymakers to make better use of the continent's agricultural resources. "Farmers need to know when to invest, and when to hold back," says Sanginga, who is involved with the mapping project.

  There's a limit, however, to our ability to adapt to climate change — we still need to reduce carbon emissions, sharply and soon. If we fail, a warmer future won't just be uncomfortable, it will be downright frightening. "We need to wake up and take care of this," says Naylor. "We won't have enough food to feed the world today, let alone tomorrow."









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