Global nitrogen footprint mapped for first time

Global nitrogen footprint mapped for first time

Four countries cause almost half the world's nitrogen emissions, pollution from foreign demand.

The first-ever global nitrogen footprint, encompassing 188 countries, shows that the U.S., China, India and Brazil are responsible for almost half of the world's nitrogen emissions, according to research conducted in Australia.

The international collaboration, led by the University of Sydney's Integrated Sustainability Analysis team, found that developing countries tend to have large amounts of nitrogen emissions embodied in their exports of food, textiles and clothing.

Nitrogen international trade routes and intensity. Source: University of Sydney

The economic modeling, which grouped the nitrogen footprint into top-ranking bilateral trade relationships, noted a trend for increased nitrogen production and found that developed nations are largely responsible for emissions abroad for their own consumption.

Doctoral candidate Arunima Malik, who co-authored the paper with University of Sydney colleagues Manfred Lenzen and Arne Geschke, as well as two researchers from Yokohama National University and one from Kyushu University in Japan, said significant nitrogen net importers were almost exclusively developed economies.

"High-income nations are responsible for more than 10 times the emissions of the poorest nations," Malik said. "This reflects greater consumption of animal products, highly processed foods and energy-intensive goods and services."

The vast bulk of emissions came from industries such as agriculture, transportation and energy generation. Emissions from consumer end use were mostly from sewage.

A paper on the research was published in the international journal Nature Geoscience.

Nitrogen pollution is becoming an increasingly significant problem as countries not only consume the naturally occurring element but also produce greater quantities of synthetic nitrogen, Lenzen said. New work by the University of Sydney looking at trends is expected to be completed soon.

"Polices are needed to integrate nitrogen supply-chains globally in order to reduce pollution," Lenzen added. "We know nitrogen emissions are increasing — just as carbon emissions are increasing as populations expand. We are now analyzing the trends, such as increased affluence and consumption, and looking at the various industries responsible for nitrogen pollution."

Findings of the 2010 research include:

* Consumption in the U.S., China, India and Brazil is responsible for 46% of global nitrogen emissions.

* Japan and other developed nations import reactive nitrogen embodied in Chinese-made clothing as well as U.S. and Australian meat.

* The U.K., Germany, Italy and France exchange significant amounts of nitrogen emissions embodied in food products.

* Hong Kong's nitrogen imports are primary agricultural and raw food products because it lacks land to produce its own livestock and crops.

* Developing countries such as China, India, Pakistan and Thailand have large amounts of nitrogen emissions embodied in their exports of textiles and clothing.

* High-income exceptions are Australia, New Zealand and Argentina, which export significant nitrogen embodied in livestock products.

* Per capita nitrogen emission ranged from more than 100 kg annually for wealthy nations such as Hong Kong and Luxembourg to less than 7 kg for developing nations such as Papua New Guinea, Cote d'Ivoire and Liberia.

* Of the 189 teragrams (Tg) of nitrogen emitted worldwide in 2010, 161 Tg were emitted from industries and agriculture, and 28 Tg were emitted by consumers.

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