Developing countries now contribute more than half of global emissions, and this share is growing at a fast pace. But, most of the world's emissions come disproportionately from the wealthy citizens of the world, irrespective of their nationality. We estimate that in 2008, half of the world's emissions came from just 700 million people. These facts encapsulate the challenge of creating an agreement that assigns fair emissions targets to nations.
Figures 1-3: A visual representation of the procedure used in the paper to determine emissions target of a country. Cartoon by Steve Pacala
The paper "Sharing Global CO2 Emissions Among One Billion High Emitters" (PDF) addresses this issue and provides a new framework for a global climate change treaty. National emissions targets are derived by summing the excess emissions of all "high emitter" individuals in a country-"high emitters" are those whose emissions exceed a universal "individual emissions cap."
Once the world agrees on a global emissions trajectory based on a stabilization target (2 °C, for example), we need a framework to come up with national allocations. Suppose we could measure every global citizen's annual emissions and line them in increasing order according to their emissions. Suppose that the global emissions target for a certain year can be met if we cap all individual emissions at a certain level. This gives us the universal "individual emissions cap" for that year. We can obtain national emissions targets using the individual emissions cap and a similar procedure at the national level. The idea is illustrated in Figures 1-3 on right.
A global emissions target of say 30 billion tons in 2030, instead of a "Business As Usual" (BAU) projection of 42 Billion tons would imply an "individual emissions cap" of 10.8 tons of CO2 to meet the target. About 1.1 billion people are affected by the cap, almost equally divided between U.S., China, other developed countries (rest of the OECD), and the rest of the world. Nations with a large number of high emitters, like the U.S. or Australia, have a more stringent target.
Our procedures requires estimates of individual emissions, and projections of BAU CO2 emissions and population. We estimate, at the national level, every individual's annual emissions using income distribution data from the World Bank and a statistically derived country specific relation between income and emissions using U.S. Energy Information Agency (EIA) emissions data. We use projections of national CO2 emissions and population, out to 2030, from EIA and UN, respectively.
The proposal also shows that addressing the energy needs of the world's poor does not make the job of managing global warming substantially difficult. Providing a floor of 1 ton of CO2 emissions per year for the poorest 2.7 billion people brings down the emissions cap from 10.8 to 9.6 tons of CO2.
This proposal provides a way of apportioning the job of emissions reduction to nations based on the emissions of their high emitting rich citizens. We intend the approach to provide national emissions targets, not a literal interpretation of the rule - that might be very hard to implement. The nations are free to implement their policies to meet the emissions targets, though it is important to do so in a equitable manner. One very important feature is straightforward rule of using a universal individual emissions cap to deal with the emissions of both developed and developing nations. As developing nations grow economically, and become more capable, they shoulder a larger fraction of the emissions reduction.