Rigorous classification and carbon accounting principles for low and Zero Carbon Cities

CO(2) emissions from the burning of fossil fuels are the primary cause of global warming. Much attention has been focused on the CO(2) directly emitted by each country, but relatively little attention has been paid to the amount of emissions associated with the consumption of goods and services in each country. Consumption-based accounting of CO(2) emissions differs from traditional, production-based inventories because of imports and exports of goods and services that, either directly or indirectly, involve CO(2) emissions. Here, using the latest available data, we present a global consumption-based CO(2) emissions inventory and calculations of associated consumption-based energy and carbon intensities. We find that, in 2004, 23% of global CO(2) emissions, or 6.2 gigatonnes CO(2), were traded internationally, primarily as exports from China and other emerging markets to consumers in developed countries. In some wealthy countries, including Switzerland, Sweden, Austria, the United Kingdom, and France, >30% of consumption-based emissions were imported, with net imports to many Europeans of >4 tons CO(2) per person in 2004. Net import of emissions to the United States in the same year was somewhat less: 10.8% of total consumption-based emissions and 2.4 tons CO(2) per person. In contrast, 22.5% of the emissions produced in China in 2004 were exported, on net, to consumers elsewhere. Consumption-based accounting of CO(2) emissions demonstrates the potential for international carbon leakage. Sharing responsibility for emissions among producers and consumers could facilitate international agreement on global climate policy that is now hindered by concerns over the regional and historical inequity of emissions. Show more

The world's population is now over 50% urban, and cities make an important contribution to national greenhouse gas (GHG) emissions. Many cities are developing strategies to reduce their emissions. Here we ask how and why emissions differ between cities. Our study often global cities shows how a balance of geophysical factors (climate, access to resources, and gateway status) and technical factors (power generation, urban design, and waste processing) determine the GHGs attributable to cities. Within the overall trends, however, there are differences between cities with more or less public transit while personal income also impacts heating and industrial fuel use. By including upstream emissions from fuels, GHG emissions attributable to cities exceed those from direct end use by upto 25%. Our findings should help foster intercity learning on reducing GHG emissions. Show more