A team of researchers from the universities of Leeds and York has discovered that anthropogenic (human-made) air pollution from North America causes Europe to lose 1.2 million tonnes of wheat a year. The scientists have said their research shows for the first time the extent of the Northern Hemisphere's intercontinental crop losses caused by ozone - a chemical partly produced by fossil fuels.

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The researchers themselves said their findings have important implications for international strategies to tackle global food shortages, as well as global climate and human health strategies. The research, published in the journal Biogeosciences, shows how ozone pollution generated in each of the Northern Hemisphere's major industrialised regions (Europe, North America and South East Asia) damages six important agricultural crops (wheat, maize, soybean, cotton, potato and rice) not only locally, but also by travelling many thousands of kilometres downwind.

Of the yield losses to Europe caused by ozone, pollution originating from North America is responsible for a 1.2 million ton annual loss of wheat. This is the biggest intercontinental ozone-related impact on any food crop. The scale of the impact of North American pollution on European wheat has previously been unknown.

Researchers calculated projected levels of surface ozone concentration, using computer modelling. Ozone is a powerful air pollutant, which is harmful to human health and vegetation (it inhibits plant growth). The concentrations studied by the scientists from Leeds are produced through a chemical combination of hydrocarbon compounds and nitrogen oxides, created by burning fossil fuels.

Using crop location and yield calculations, the research team was able to predict impacts of pollution on staple food crops, each with their own unique sensitivity to ozone pollution.

Dr Lisa Emberson a senior lecturer from the University of York's Stockholm Environment Institute and Environment Department, said, "This study highlights the need for air pollution impacts on crops to be taken more seriously as a threat to food security; currently air quality is often overlooked as a determinant of future crop supply Given the sizeable yield losses of staple crops caused by surface ozone, coupled with the challenges facing our ability to be food secure in the coming decades further coordinated international  efforts should be targeted at reducing emissions of ozone forming gases across the globe."

Dr Steve Arnold, a senior lecturer in atmospheric composition at the University of Leeds's School of Earth and Environment, who led the study, said, "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."

The researchers also found that:

• In terms of global crop losses, Asian pollution dominates worldwide losses of wheat (50-60per cent) and rice (more than 90per cent).
• North American pollution contributes the most to worldwide losses of maize (60-70 per cent) and soybean (75-85per cent).
• The impact of Europe's pollution on other continents is minor due to fewer low pressure systems and weather fronts, which are responsible for transporting pollution across continents.

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