Crop yields in the United States — the world's largest exporter of agricultural products — could fall as much as 82 per cent by 2100 if temperatures rise sharply, according to a new study.
Wolfram Schlenker and Michael Roberts, American researchers, studied the impact of varying growing-season temperatures on corn, cotton and soybean yields in the US. They used agricultural records and detailed weather data collected between 1950 and 2005.
They found a nonlinear relationship between temperature and productivity: yields increased modestly until a threshold temperature was reached at 29 °C for corn, 32 °C for cotton and 30 °C for soybean. Past these stated temperatures the yield dropped off sharply. This was true for all regions of the US, including the warmer southern states.
On average there are 57 days in a year that exceed 29°C. Schlenker and Roberts moddelled for future climite change finding that the number of days exceeding 29 °C in a growing season could rise to 413 by the end of the century if we do not cut our greenhouse emissions. This is of course the worst case scenario, but were it to happen maize yields would fall by 82 per cent! Even if we reduce emissions by 50 per cent by 2050, relative to 1991 levels - a target which governments are struggling to agree on and optimistic by the looks of it - yields could still fall by between 30 and 46 per cent.
The silver lining for all us that want to avoid food shortages and the inevitable price hikes is that potential gains in productivity due to raised CO2 concentrations were not taken into account, this rise will likely partially offset any decline in yield due to warming.
Reference
Schlenker, W. and Roberts, M.J. (2009) Nonlinear temperature effects indicate severe damages to U.S. crop yields under climate change. Proceedings of the National Academy of Sciences, 106(37): 15594-15598
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