This map shows the flow of carbon emissions embodied in trade among the major exporting and importing countries. Net exporting countries are in blue and net importers in red. China is by far the largest exporter of carbon dioxide emissions. Arrows indicate direction and magnitude of flow; numbers are megatonnes. (Steven Davis/Carnegie Institution for Science)

Developed countries are "outsourcing" more than a third of their carbon emissions associated with products and services to other countries, researchers say.

A study of trade data found that some countries in Western Europe have more than half of their total carbon dioxide emissions occurring elsewhere, especially in developing countries such as China.

Reserachers at the Carnegie Institution used trade data from 2004 to create a model of the global flow of products in 113 countries and regions.

They then associated those products with carbon emissions to determine which countries are net "importers" of emissions and which are net "exporters."

"Just like the electricity that you use in your home probably causes CO2 emissions at a coal-burning power plant somewhere else, we found that the products imported by the developed countries of western Europe, Japan, and the United States cause substantial emissions in other countries, especially China," said the study's lead author Steven Davis of Carnegie, in a statement.

The study, published this week in the Proceedings of the National Academy of Sciences, found that, per person, products consumed in Europe caused almost four tonnes of carbon emissions in other parts of the world.

In the U.S., the figure was smaller, about 2.2 tonnes per person, although the U.S. is both a major importer and exporter of carbon emissions. The U.S. "outsources" about 11 per cent of its total emissions associated with consumption of products.

Canada, while mentioned as a country with relatively high per capita production of carbon emissions, has a small net export of emissions, along with Australia, Indonesia, the Czech Republic, and Egypt.

The study said the carbon emissions associated with Canada's imports and those associated with its exports are roughly the same, at about 100 megatonnes per year.

The researchers say their works shows that carbon emissions policy must take total emissions into account, not just the domestic emissions of each country.

"This could be taken into consideration when developing emissions targets for these countries, but that's a decision for policy-makers," said Ken Caldeira, a researcher in the Carnegie Institution's Department of Global Ecology.

"One implication of emissions outsourcing is that a lot of the consumer products that we think of as being relatively carbon-free may in fact be associated with significant carbon dioxide emissions," he said.

Davis said the source country for carbon emissions ultimately doesn't matter.

"Effective policy must have global scope," he said. "To the extent that constraints on developing countries' emissions are the major impediment to effective international climate policy, allocating responsibility for some portion of these emissions to final consumers elsewhere may represent an opportunity for compromise."