“THE PROMISE of food lies in the tropics,” the UN Food and Agriculture Organization director general said at the University of the Philippines. “Here in this sun-drenched belt of land, temperature is benign and rainfall abundant. These could be the food granaries for the world of our children.”
Not anymore. Rising temperatures have widened the “Tropical Belt,” notes Nature Geoscience. Since the FAO official delivered his address in Los Baños in May 1979, the tropics expanded by between 2 and 4.8 degrees latitude. As the world warms, edges of the “Belt”—outer boundaries of the subtropical dry zones—drift toward the poles.
Temperature and rainfall changes are altering yields. Affected are politically volatile crops like corn and rice. “In the Philippines, rice yields drop by 10 percent for every one degree centigrade increase in night-time temperature,” BBC’s environment correspondent Richard Black writes.
The slump is region-wide. As droughts dry reservoirs, yields have fallen by 10 to 20 percent over the last 25 years. More declines are ahead.
“We found that as the daily minimum temperature increases, or as nights get hotter, rice yields drop,” researcher Jarrod Welch said. “Where temperature increases more than 3 °C, impacts are stressful to all crops and in all regions,” the Intergovernmental Panel on Climate Change (IPCC) concluded.
There are biological limits to what can be done. “We can’t just move all our crops north or south because a lot of crops are photosensitive,” notes Dr. Geoff Hawtin at the International Center for Tropical Agriculture. “Flowering is triggered by day length.”
We don’t know where the tipping points are,” Hawtin adds. “They could come quite quickly.”
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