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Open Access Publications from the University of California

Accounting for carbon dioxide emissions: A matter of time


Carbon dioxide emissions in one country can support consumption of goods and services in another country; countries and their CO2 emissions are linked together by international trade. The study of CO2emissions embodied in international trade was largely opened up by Peters and Hertwich (1). In PNAS, Peters et al. (2) introduce a dimension into this field of study, and that dimension is time. It is not often that one team of researchers has done so much to introduce a field of inquiry and then expand it so rapidly, giving us insights into the challenges and potential solutions to the energy/carbon/climate problem we all face.

On any typical day, we engage in a wide range of activities that are supported by CO2 emissions, either directly or indirectly. When we drive our cars to work, CO2 comes out of the tailpipe—a waste product resulting from the reaction of gasoline with atmospheric oxygen inside of an internal combustion engine. So, how much CO2 was released to the atmosphere to get us to work this morning? Counting just the CO2 that comes out of the tailpipe would fail to consider the fact that CO2 was emitted to extract, refine, and transport that gasoline to us. The automobile is composed of steel and rubber, aluminum and plastic; CO2 was released to supply the energy needed to manufacture each of these materials. Furthermore, the factories that produced the automobile had machines of various sorts, and the energy it took to make these machines likely produced CO2 emissions as well. Furthermore, the workers in factories that made all of these things may have driven cars to get themselves to work. What part of their CO2 emissions was emitted to facilitate our morning commute?

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