"If we begin by asking, “Why should anyone have a greater claim to part of the global atmospheric sink than any other?” then the first, and simplest response is: “No reason at all.” Everyone has the same claim to part of the atmospheric sink as everyone else. This kind of equality seems self-evidently fair, at least as a starting point for discussion.
The Kyoto Protocol aimed to achieve a level for developed nations that was 5 percent below 1990 levels. Suppose that we focus on emissions for the entire planet and aim just to stabilize them. If we choose a target of 1996 emissions levels, then the allocation per person works out conveniently to about 1 metric ton of carbon per year. This becomes the basic equitable entitlement for every human being on the planet. (Note that emissions are sometimes expressed in terms of tons of carbon dioxide, rather than tons of carbon. One ton of carbon is equivalent to 3.7 tons of carbon dioxide.)
Now compare actual emissions for some key nations. In 2004, the United States produced 5.61 tons of carbon per person per year, while Japan, Germany and the U.K. each produced less than 3 tons. China was at 1.05 and India at 0.34. This means that to reach an equal per capita annual emission limit of 1 ton, India would be able to increase its emissions three times. China, on the other hand, would need to stabilize its current emissions, and the United States would have to reduce its emissions to one-fifth of present levels.
One objection to this approach is that it gives countries an insufficient incentive to do anything about population growth. We can meet this objection by setting national allocations that are tied to a specified population, rather than letting them rise with an increase in population.
But since different countries have different proportions of young people about to reach reproductive age, this provision might produce greater hardship in countries that have younger populations. To overcome this, the per capita allocation could be based on an estimate of a country’s population at some future date. Countries would then receive a reward in terms of an increased emission quota per citizen if they achieved a lower population than had been expected.
Each of these principles of fairness, or others, could be defended as the best one to take. I propose, both because of its simplicity, and hence its suitability as a political compromise, and because it seems likely to increase global welfare, that we support the principle of equal per capita shares of the capacity of the atmospheric sink, tied to the current projections of population growth per country for 2050.
Some will say that this is excessively harsh on industrialized nations, which will have to cut back the most on their output of greenhouse gases. Yet the one person, one share principle is more indulgent to the industrialized nations than some other others, including the historical principle.
Allocating on the basis of equal per capita shares will be tremendously dislocating for the industrialized nations, and the mechanism of emissions trading can make this transition much easier. Emissions trading works on a simple economic principle: If you can buy something more cheaply than you can produce it yourself, you are better off buying it than making it. In this case, what you can buy will be a transferable quota to produce greenhouse gases, allocated on the basis of an equal per capita share.
The ancient Greek iconoclast Diogenes, when asked what country he came from, is said to have replied: “I am a citizen of the world.” Until recently, such thoughts have been the dreams of idealists. But now we are beginning to live in a global community. The impact of human activity on our atmosphere exemplifies the need for human beings to act globally. On this issue, as well as others, the planet should become the basic unit for our ethical thinking." (http://www.peopleandplace.net/featured_voices/2009/3/25/%E2%80%9Cone_person_one_share%E2%80%9D_of_the_atmosphere)