Scientists analyse effects of global warming, atmospheric ozone on crops

Monday, July 28, 2014 

A research team from the Massachusetts Institute of Technology and Colorado State University of the US and the University of Sheffield of the UK has analysed effects of global warming and ozone pollution over 2000–2050 on the worldwide production of wheat, rice, maize and soybean. The study was published in journal Nature Climate Change yesterday.

The scientists found reduction of crop yields by 2050 exceeded 10% of 2000 levels, substantially decreasing food security, in all cases examined. Several scenarios were considered because of uncertainty of future levels of ozone pollution. They estimated by 2050, increasing population and changing diet would increase world food needs by 50 percent. As coauthor Colette Heald told The Huffington Post, “The climate projections are quite consistent […] the future of ozone pollution is very different […] leading to either offsetting or reinforcing effects [of climate change] on crops”. By 2050, undernourishment would increase by either 49 percent or by 27 percent, depending on the scenario.

The study focuses on ozone–temperature covariation: ground-level ozone increases with temperatures. Heald said although temperature and ozone are separately known to impact crop yields, “nobody has looked at these together”. Depending on region and crops, the yields may be primarily sensitive to ozone —in the case of wheat— or heat —in the case of maize— alone, providing a local estimation of relative benefits of climate change adaptation versus ozone regulation.

The U.S. Department of Agriculture notes, “Ground-level ozone causes more damage to plants than all other air pollutants combined”, highlighting the importance of air quality for agriculture. Results of NCLAN studies, published in a paper by AS Heagle in 1989, show dicot species, such as soybean, cotton, and peanut, lose more yield from ozone than do monocot species such as sorghum, field corn, and winter wheat. The researchers found that ozone pollution caused 46 percent of previously heat-attributed damage to soybean crops.

The model does not include the effect of rising carbon dioxide concentration, which has complex and potentially offsetting impacts on global food supply. The U.S. Environmental Protection Agency says some crops may have higher yields with increased levels of carbon dioxide. However, global warming also increases probability of extreme crops-damaging weather events such as floods, droughts, and extreme temperatures. Climate change affects distribution of weeds, pests, and diseases. Heald noted the findings show pollution reduction is also important. “An air-quality cleanup would improve crop yields […] Ozone is something that we understand the causes of, and the steps that need to be taken to improve air quality.”

As Heald told The Huffington Post, US surface ozone has dropped partly due to the Clean Air Act. “Despite an increase in vehicle miles driven and energy consumption, surface ozone has declined by 25 percent on average across the U.S. from 1980 to 2012 […] However, the future of ozone air quality in the U.S. and around the world will depend on local emissions, the use of pollution control technology, regulations, and air quality policy.”

The study was supported by the Croucher Foundation, US National Science Foundation, and US National Park Service.