Many people have asked how a country’s carbon footprint  compares to the territorial emissions reported to the United Nations  Framework Convention on Climate Change (UNFCCC)?

In hindsight, it was perhaps remiss of us not to include this data in the paper. However, it was not our motivation.

Focusing on whether the emissions are bigger or smaller misses a  large part of the story. The main focus of the paper is on what  consumption categories cause emissions and how this varies across  countries with different incomes. The current approach in the UNFCCC  reveal what the emissions are from electricity, transportation, and so  on. This is vital information, however, only a carbon footprint can  reveal what the emissions are to produce food, car, television, or to  get a hair cut. This information is needed by consumers if they want to  reduce their own personal footprint (http://www.springerlink.com/content/1976p75463860416/).  The real value of a carbon footprint is the information it reveals, not  necessarily if the footprint is bigger or smaller than the territorial  emissions.

In a broader global perspective, if a country’s carbon footprint  grows over time relative to territorial emissions then it means that the  country is increasingly importing products at the expensive of domestic  production. If that country has an emission limitation in the Kyoto  Protocol and the imports are coming from countries without emission  limitations then global emissions may increase while it “appears”  emissions are decreasing. This is known as carbon leakage (http://www.nature.com/climate/2008/0804/full/climate.2008.25.html).

In fact, this is what is happening now. Since 1990 the emissions in  countries with an emission limitations have largely stabilized, while  the emissions in countries without emission limitations have increased  about 80%. The main reason for this is the explosive growth of China,  however, recent research has shown that about 50% of the growth in  Chinese emissions since 2000 is due to the production of products  exported from China and consumed in other countries (http://www.agu.org/pubs/crossref/2009/2008GL036540.shtml).

An analysis of the carbon footprint is useful for an analysis of carbon leakage, but the footprint better measured another way (http://dx.doi.org/10.1016/j.ecolecon.2007.10.014).  The carbon footprint in our article only directly considers trade to  final consumers (such as households) and trade to industry is calculated  internally in the model. Thus, the footprint of the USA includes  emissions that occur to extract iron-ore in Australia, to produce steel  in China, to produce a car in Japan, which is consumed in the USA. While  this is perfectly logically, it means that the imported emissions are  not directly comparable to the import statistics which only consider the  first trading partner (the trade from Australia to China is not  included in the US trade statistics). To make trade statistics and  imported emissions consistent it is more intuitive to consider only the  first link in the supply chain, but include imports to both industry and  final consumers. This method was used in another of our papers (http://pubs.acs.org/doi/abs/10.1021/es072023k) and we call a Consumption-Based Inventory.

In the two different approaches the imported emissions differ, but  the exported emissions need not differ if the arithmetic is done  correctly. In the Carbon Footprint of Nations paper, the imported  emissions cover the global emissions required to produce the final  consumption in each country, while in a Consumption-Based Inventory the  imported emissions cover the domestic emissions in each country to  produce total (final and industry) consumption in each country. If trade  to industry and final consumers is include, then only domestic  emissions are included to avoid double counting.

Both approaches do lead to some confusion, but they serve a different  purpose. A Carbon Footprint tells us what consumption categories are  important and how we may reduce emissions by consuming differently. The  Consumption-Based Inventory focuses on trade relationships and how the  trade relationships redistributed emissions between countries. Depending  on the question being asked, one method is usually preferred.