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"Sharing Global CO2 Emission Reductions Among One Billion High Emitters"

Visitors look at a piece of insulated glass installed on a model house during an energy-saving exhibition in Xiamen, SE China's Fujian province, June 6, 2009.
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"Sharing Global CO2 Emission Reductions Among One Billion High Emitters"

Journal Article, Proceedings of the National Academy of Sciences of the United States of America

July 6, 2009

Authors: Shoibal Chakravarty, Ananth Chikkatur, Former Associate, Energy Technology Innovation Policy research group, Heleen de Coninck, Stephen Pacala, Robert Socolow, Massimo Tavoni

Belfer Center Programs or Projects: Energy Technology Innovation Policy; Environment and Natural Resources; Science, Technology, and Public Policy



We present a framework for allocating a global carbon reduction target among nations, in which the concept of "common but differentiated responsibilities" refers to the emissions of individuals instead of nations. We use the income distribution of a country to estimate how its fossil fuel CO2 emissions are distributed among its citizens, from which we build up a global CO2 distribution. We then propose a simple rule to derive a universal cap on global individual emissions and find corresponding limits on national aggregate emissions from this cap. All of the world's high CO2-emitting individuals are treated the same, regardless of where they live. Any future global emission goal (target and time frame) can be converted into national reduction targets, which are determined by "Business as Usual" projections of national carbon emissions and in-country income distributions. For example, reducing projected global emissions in 2030 by 13 GtCO2 would require the engagement of 1.13 billion high emitters, roughly equally distributed in 4 regions: the U.S., the OECD minus the U.S., China, and the non-OECD minus China. We also modify our methodology to place a floor on emissions of the world's lowest CO2 emitters and demonstrate that climate mitigation and alleviation of extreme poverty are largely decoupled.


The 1992 United Nations Framework Convention on Climate Change (UNFCCC) created a 2-tier world. It called upon the developed ("Annex I") countries to "take the lead" in reducing carbon emissions, and, under the principle of "common but differentiated responsibilities," established no time frame for developing countries to follow. However, a consensus is now emerging in favor of low stabilization targets. These targets cannot be achieved without the participation of developing countries, which today emit about half of global CO2 emissions and whose future emissions increase faster than the emissions of industrialized countries under "business as usual" scenarios.

On what terms should developing countries participate? There are many proposals, each buttressed by some appeal to "fairness." Per capita allocation is widely acknowledged to represent the only equitable goal in the long term, but intermediate steps are required in the short-to-medium term. Uniform percentage reductions in emissions across all countries are rightly rejected by all parties, on the grounds that industrialized countries must create headroom for developing countries. Here, we offer a different approach: An allocation of national targets for fossil-fuel CO2 emissions derived from a fairness principle based on the "common but differentiated responsibilities" of individuals, rather than nations. Our proposal moves beyond per capita considerations to identify the world's high-emitting individuals, who are present in all countries....

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For Academic Citation:

Chakravarty, Shoibal, Ananth Chikkatur, Heleen de Coninck, Stephen Pacala, Robert Socolow, and Massimo Tavoni. "Sharing Global CO2 Emission Reductions Among One Billion High Emitters." Proceedings of the National Academy of Sciences of the United States of America (July 6, 2009).

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