A synthesis of carbon in international trade.

In a globalised world, the transfer of carbon between regions, either physically or embodied in production, represents a substantial fraction of global carbon emissions. The resulting emission transfers are important for balancing regional carbon budgets and for understanding the drivers of regional emissions. In this paper we synthesise current understanding in two parts: (1) embodied CO₂ emissions from the production of goods and services produced in one country but consumed in others, (2) physical carbon flows in fossil fuels, petroleum-derived products, harvested wood products, crops, and livestock. We describe the key differences between studies and provide a consistent set of estimates using the same definitions, modelling framework, and consistent data. We find the largest trade flows of carbon in international trade in 2004 were fossil fuels (2673MtC, 37% of global emissions), CO₂ embodied in traded goods and services (1661MtC, 22% of global emissions), livestock (651MtC, 20% of total livestock carbon), crops (522MtC, 31% of total harvested crop carbon), petroleum-based products (183MtC, 50% of their total production), and harvested wood products (149MtC, 40% of total roundwood extraction). We find that for embodied CO₂ emissions estimates from independent studies are robust. We found that differences between individual studies is not representative of the uncertainty in consumption-based estimates as different studies use different production-based emission estimates as input and different definitions of allocating emissions to international trade. After adjusting for these issues, results across independent studies converge to give less uncertainty than previously assumed. For physical carbon ?ows there are relatively few studies to be synthesised, but differences between existing studies are due to the method of allocating to international trade with some studies using "apparent consumption" as opposed to "final consumption" in more comprehensive approaches. While results across studies are robust to be used in further applications, more research is needed to understand the differences between methods and to harmonise definitions for particular applications. [ABSTRACT FROM AUTHOR]