A warning says that extreme heat waves, which have intensified in recent years, are pushing the global food system to the brink of collapse.
On the 23rd, the Food and Agriculture Organization of the United Nations (FAO) and the World Meteorological Organization (WMO) said in a jointly authored report that heat waves have pushed food supply chains in some regions to their limits. According to the WMO, last year the global average temperature rose 1.43 degrees compared with the preindustrial period (1850–1900), sending Earth's energy imbalance to its highest level in 65 years of observations.
According to the report, in India and most of South Asia, the tropical regions of sub-Saharan Africa, and parts of Central and South America, farmers are expected to be unable to work outdoors for up to 250 days a year (about two-thirds of the year) due to heat waves.
Heat waves also raise livestock mortality. Typical livestock begin to experience heat stress at around 25 degrees. Extreme heat reduces milk yields in dairy cows and lowers the fat and protein content of milk. Pigs and chickens, which cannot sweat, can suffer digestive tract damage, organ failure, and cardiovascular shock as temperatures rise.
Crop yields also appear set to decline. For most crops, yields fall once temperatures exceed 30 degrees. That is because cell walls weaken and toxic substances are produced, degrading quality. According to the report, in some regions corn production has already fallen by about 10%, and wheat has declined by a similar level. The report warned that if the temperature rise exceeds 1.5 degrees compared with the preindustrial period, crop yields will fall further.
The report said that because heat waves are to a large extent predictable, there is a need to strengthen warning systems for farmers. Using weather forecasts and mobile communications, authorities can alert them in advance to expected periods of extreme heat.
Richard Waite, director of the agriculture initiative at the World Resources Institute (WRI), said, "If we do not respond to climate change, heat waves will reduce crop and livestock output, and more land will be put into agriculture to maintain food production," adding, "This will increase greenhouse gas emissions from land-use change, creating a vicious cycle that worsens the climate impacts on agriculture."
The report also suggested that the food crisis could spread beyond some hot countries to become global. Tim Lang, an emeritus professor of food policy at the University of London, said that temperate regions and advanced economies will not be spared.
Lang said, "The acceleration of climate uncertainty is becoming a serious challenge for food producers worldwide," adding, "Regions that used to import food will become drier, land use will change, and dependence on water resources will be exposed." He also warned, "Crops that initially grow well will ultimately fail to mature, productivity will falter, and established patterns of cultivation and consumption will change."