Rebecca Renner/Pennsylvania, US

When it comes to carbon dioxide emissions, the industrialised world appears to be cleaning up its act - over the last decade countries like the UK and the US have reduced their outpourings of this greenhouse gas. But at the same time CO₂ emissions in developing countries, especially China, have soared. And in 2008, China overtook the US as the world's largest carbon dioxide emitter. An important reason for this shift is that industrialised countries 'outsource' a large proportion of the carbon dioxide emissions associated with manufacturing the items they consume, according to a new study that, for the first time, details this outsourcing on a global basis.

'The planet doesn't care where CO₂ is emitted,' says lead author Steven Davis at the Carnegie Institution in Stanford. 'If we congratulate ourselves for national reductions in carbon dioxide emissions and fail to realise we've shifted them somewhere else, we are deluding ourselves,' he says. 

Davis and colleague Ken Caldeira used published trade data from 2004 to create a global model for the flow of products that range from electronics to vegetable oil between 113 countries or regions. By allocating carbon emissions to particular products and sources, the researchers were able to calculate the net emissions 'imported' or 'exported' by specific countries.

Over a third of the carbon dioxide emissions linked to goods and services consumed in many European countries occurred elsewhere, they found. In Switzerland and several other small countries, outsourced emissions exceeded the amount of carbon dioxide emitted within national borders. The US is both a major importer and a major exporter of emissions embodied in trade. The net result is that the US outsources about 11 per cent of total consumption-based emissions, primarily to the developing world. 

'The importance of the study is in showing that although the developing world has passed the developed world in location-based emissions of CO₂, a portion of these emissions are actually the responsibility of the developed world,' says Christopher Weber, an expert in the environmental implications of international trade at Carnegie Mellon University in Pittsburgh, US. 'China's emissions in particular have shot up but these are due in large proportion to exports to the global west, which is important for the climate blame game happening in global negotiations,' he says. 

Global regulations may not be the way to acknowledge these outsourced or 'embedded' emissions, says Iain Watt at Forum for the Future, a UK research group that advises business on sustainability. Leading corporations like Tesco and Walmart intend to label their products in terms of embedded carbon. 'To sell in a world that takes climate change seriously companies need to find a way to deal with embedded emissions,' he says.