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Please quote Nature Geoscience as the source of these items.

January 2016

Developed nations outsource part of nitrogen emissions to developing countries

Roughly one quarter of global nitrogen emissions come from the production of goods and commodities that are consumed outside their country of origin, reports a paper published online this week in Nature Geoscience. The study quantifies the amount of nitrogen pollution generated for 188 countries and suggests that net importers of these goods and commodities (importing more than they export) are almost exclusively in the developed world, whereas the countries where the related production—and therefore pollution—occurs are often developing economies.

Reactive nitrogen gases produced from combustion and agriculture can contribute to air pollution, climate change and acid rain, and nitrate from fertilizers can pollute groundwater or create dead zones in lakes and coastal regions.

Manfred Lenzen and colleagues used an economic model and estimates of reactive nitrogen emissions from the production, transportation and consumption of commodities to quantify the amount of nitrogen emissions caused by a country's consumption—for 188 countries, across nearly 15,000 economic sectors. They show that consumption in Brazil, China, India and the United States is responsible for nearly half (47%) of the world's commodity-related nitrogen emissions (approximately 89 million tonnes). Finally, the authors find that consumption of foreign-produced goods is so great in some countries that they cause more nitrogen pollution in other nations than they do in their own.

In an accompanying News & Views article, James Galloway and Allison Leach write that Lenzen and colleagues reveal "the degree to which we may be, in effect, exporting our nitrogen pollution to other countries".

Substantial nitrogen pollution embedded in international trade

Azusa Oita, Arunima Malik, Keiichiro Kanemoto, Arne Geschke, Shota Nishijima & Manfred Lenzen

Published online: 25 January 2016 | doi 10.1038/ngeo2635

Sustainability: Your feet's too big

James N. Galloway & Allison M. Leach

Published online: 25 January 2016 | doi 10.1038/ngeo2647

Giant icebergs leave trail of carbon sequestration in their wake

Melting water from giant icebergs, which contains iron and other nutrients, supports phytoplankton growth that is responsible for as much as 20% of the carbon sequestered to the depths of the Southern Ocean by biological metabolism and growth, reports a study published online this week in Nature Geoscience. These giant icebergs, dozens of which are floating in the Southern Ocean at one time, influence phytoplankton over an area ten times larger than typical icebergs do, even when accounting for the difference in size.

The Southern Ocean plays a significant part in the global carbon cycle, and is responsible for approximately 10% of the ocean's total carbon sequestration through a mixture of biologically driven and chemical processes, including phytoplankton growth. However, previous studies have suggested that ocean fertilization from icebergs—in the form of iron and other micronutrients from meltwater—makes relatively minor contributions to phytoplankton uptake of CO2, some of which is subsequently sequestered in the deep ocean.

Grant Bigg and colleagues analysed satellite images of ocean colour—an index of phytoplankton productivity at the ocean's surface—associated with a range of icebergs at least 18 km in length in the open Southern Ocean. They find enhanced phytoplankton productivity extends hundreds of kilometres from giant icebergs, and persists for at least one month after an iceberg passes. The authors suggest their new analysis reveals that giant icebergs may play an outsize role in the Southern Ocean carbon cycle.

Enhanced Southern Ocean marine productivity due to fertilization by giant icebergs

Luis P. A. M. Duprat, Grant R. Bigg & David J. Wilton

Published online: 11 January 2016 | doi 10.1038/ngeo2633

Clouds double El Niño amplitude

The influence of clouds on the atmospheric circulation accounts for more than half of the strength of El Niño and La Niña events, suggests a study published online in Nature Geoscience this week. The findings indicate that incorporating changes in cloud dynamics into climate models may improve our understanding of the response of El Niño/Southern Oscillation (ENSO) to climate change.

ENSO is the most significant source of weather variability on timescales of three to seven years. However, the relative importance of atmospheric and oceanic processes, and the interactions between the two, is the subject of debate.

Thorsten Mauritsen and colleagues compared climate model simulations that accounted for the interactions between clouds and atmospheric circulation with climate model simulations that did not account for these interactions. They find that the variability in sea surface temperatures associated with ENSO is at least twice as strong in the simulations that fully account for the interactions between clouds and atmospheric circulation.

Amplification of El Niño by cloud longwave coupling to atmospheric circulation

Gaby Rädel, Thorsten Mauritsen, Bjorn Stevens, Dietmar Dommenget, Daniela Matei, Katinka Bellomo & Amy Clement

Published online: 4 January 2016 | doi 10.1038/ngeo2630


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