Nitrogen international trade routes and intensity. Credit Source: University of Sydney. Click to EnlargeThe global environmental movement has focused largely on the carbon footprint, and the potential dangers of global warming.

But the global nitrogen footprint, which also impacts human and environmental health, has never been cataloged – until now. Nitrogen emission levels closely follow international trade routes, and pose dangers to human and ecosystems alike, according to a new study in the journal Nature Geoscience.

Forty-six percent of the world’s nitrogen emissions are attributable to the United States, China, India and Brazil, according to the calculations by the scientists from the University of Sydney.

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

Developing nations, on the other hand, produce much of the nitrogen with their exports of food, textiles and clothing – but most of which is produced on behalf of the world’s richest nations. Among the biggest “exporters” of this nitrogen production are China, India, Parkistan, and Thailand.

The few high-income nations that have net exports of nitrogen emissions are Australia, New Zealand, and Argentina, due especially to their livestock cultivation for markets in other countries.

“We know nitrogen emissions are increasing – just as carbon emissions are increasing as populations expand,” said Manfred Lenzen, another author. “We are now analyzing the trends, such as increased affluence and consumption, and looking at the various industries responsible for nitrogen pollution.”

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Nitrogen can effectively choke off ecosystems, like through algal blooms in waterways preventing other life from growing or flourishing, according to the U.S. Environmental Protection Agency. Excess nitrogen can also seriously affect human health, by a variety of factors in drinking water and in breathable air.

The Nature Geoscience study references one particular ripple effect of the nitrogen cycle. The scientists analyzed the dairy and cattle industry in Tulare County, California. The majority of the residents are low-income Latinos – and a significant minority of them have been exposed to excess nitrogen from massive fertilizer use in the region. In the meantime, that single California county’s agricultural exports count for roughly a fifth of Japan’s imported nitrogen footprint from the U.S., its most important trading partner.

A fundamental shift in the economy would be needed to redirect this pollution factor, according to the researchers. But consumers are not directly causing the burden; of 189 teragrams of nitrogen (189 billion kilograms) emitted in 2010, 161 teragrams were emitted from industries and agriculture, while only 28 were emitted directly by consumers.

Sources: National Bureau of Statistics of China; Ministry of Environmental Protection (China)