Wheat-harvest
Wheat harvest in Denmark. Ozone pollution from North America reduces annual yields by 1.2 million tonnes. FLICKR/Lars Plougmann

The research, published in the journal Biogeosciences, is the first to quantify the impact of ozone pollution from each of the Northern Hemisphere’s major industrialised regions – North America, Southeast Asia, and Europe – on crop yields globally and in continents downwind of each region.

Lisa Emberson, senior research associate in SEI’s York Centre, at the University of York, worked with colleagues at the University of Leeds, U.K., to estimate the effect of ozone exposure on six major food crops: wheat, maize, soybean, cotton, potato and rice.

They found that ozone pollution causes millions of tonnes of crop losses each year – not just in the regions where it’s emitted, but across continents: Pollutants from North America reduce wheat yields in Europe by 1.2 million tonnes each year.

On a global scale, pollution from Southeast Asia has the biggest impact, the study shows, causing the loss of 6.7 million tonnes of wheat and about 11.6 million tonnes of rice each year.

“This study highlights the need for air pollution impacts on crops to be taken more seriously as a threat to food security in the coming decades,” says Emberson. “Given the sizeable yield losses of staple crops caused by surface ozone, there should be greater coordinated international efforts focused on reducing emissions of ozone-forming gases across the globe.”

Rice-crop
Rice crop, Japan. FLICKR/shop boy

A powerful pollutant

Surface ozone is produced through a chemical combination of hydrocarbons and nitrogen oxides emitted during high-temperature combustion, such as of fossil fuels. Not only does it damage vegetation by damaging cells and inhibiting plant growth, but it is also harmful to human health, particularly to the respiratory system.

The study authors used a computer model to predict reductions in global surface ozone if man-made emissions of nitrogen oxide from the three continents were shut off. Using crop location and yield calculations, they then predicted impacts on staple food crops, as well as the relative impact of pollutants emitted in different parts of the Northern Hemisphere.

They found that Southeast Asia accounts for 50 to 60 per cent of the estimated wheat crop losses, and more than 90 per cent of rice crop losses. North American pollution, in turn, contributes most to global losses of maize (60 to 70 per cent) and soybeans (75 to 85 per cent).

Pollutants from Europe have only a minor impact on other regions because weather systems do not carry them out to other continents in large quantities. However, the local impact is significant: 3.5 million tonnes of wheat lost each year (of a total of about 130 million produced).

Local action is not be enough
The key message of the study, Emberson says, is that curbing ozone pollution will produce substantial benefits, not only locally but in continents downwind. This is consistent, she notes, with the recommendations made by SEI-York researchers in a major project on short-lived climate forcers sponsored by the United Nations Environment Programme.

But the study also shows no region can solve this problem alone.

“Our findings demonstrate that air pollution plays a significant role in reducing global crop productivity, and show that the negative impacts of air pollution on crops may have to be addressed at an international level rather than through local air quality policies alone,” says Steve Arnold, a senior lecturer in atmospheric composition at the University of Leeds’s School of Earth and Environment and lead author of the study.

“With future emissions of ozone-forming chemicals from Europe and North America expected to reduce, and emissions from Asia to increase,” he adds, “the findings suggest that increasing pollution from Asia may partly offset crop production benefits gained in Europe and North America through local emission reduction strategies.”

The study was jointly funded by the Natural Environment Research Council and the Met Office in the U.K.

Read the article (external link to journal)