US still responsible for most CO2 emissions

Europeans import nearly twice as much carbon dioxide per head as US citizens – but the US still holds the dubious distinction of being the world's largest emitter

by Phil McKenna | New Scientist | 08 March 2010

The Carnegie Institution for Science in Stanford, California, reports that in 2004 23 per cent of global CO₂ emissions – some 6.2 gigatonnes – went in making products that were traded internationally. Most of these products were exported from China and other relatively poor countries to consumers in richer countries. Some countries, such as Switzerland, "outsourced" over half of their carbon dioxide emissions in this way because they have a high import-to-export ratio of such energy-intensive goods as consumer electronics, motor vehicles and machinery.

The average European is responsible for adding more than 4 tonnes of CO₂ to the atmosphere in the manufacture of goods imported from other countries. For people in the US, the figure was nearly half that – 2.5 tonnes – thanks to US exports of emissions-intensive goods that offset much of the C0₂ it imports.

The Carnegie study is one of the most comprehensive to date of a growing number that track emissions based on where goods are consumed. National inventories such as those conducted annually by the United Nations Framework Convention on Climate Change currently consider emissions produced in each country's own territory only.

Lifestyle emissions

"If we want to understand our footprint of emissions, we have to understand that others are emitting on our behalf to make our goods and services," says study co-author Ken Caldeira. "The US and Europe are responsible for a bigger percentage of emissions, because it is emissions that go into the production of goods coming out of China that are supporting our lifestyle."

The study draws on detailed economic data from the Global Trade Analysis Project based at Purdue University in West Lafayette, Indiana, which takes into account the CO₂ emissions intensity of manufacturing in different countries and different sectors of the economy.

Another study, which Glen Peters of Norway's Center for International Climate and Environmental Research in Oslo is to publish soon, uses similar trade data to analyse consumption-based emissions up to 2008 and also tracks how the global movement of CO₂ emissions has changed since 1990.

Based on Peters's findings, the US still leads the world in CO₂ emissions because although US exports offset some of its territorial emissions, taken as a whole it is still emits the most. "China surpassed the US around 2006 in terms of territorial emissions, but in terms of consumption, you'll find that the US is still the biggest emitter," he says.

Taking all 2008 imports and exports into account, US emissions increase by about 10 per cent compared with territorial emissions and China's emissions decrease by about 20 per cent for the same year, Peters says.

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0906974107

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