Overpopulation and climate change - too many Americans?

In a recent article timed to coincide with the UN Climate Summit in New York City, The Economist offered a ranking of “20 policies and courses of action according to how much they have done to reduce the atmosphere’s stock of greenhouse gases." A number of their choices were unexpected, such as the implementation of China’s one child policy.

China's 1-child policy ranks 4th in the list - allegedly preventing 1.3 billion tons of CO₂ from entering the atmosphere. This estimate is taken from a 2007 Reuters article in which "Su Wei of China’s foreign ministry said that his country’s one-child policy, by reducing the number of births between the late 1970s and the mid-2000s by 300m, had reduced carbon emissions by 1.3 billion tonnes in 2005 (because there were fewer people to consume goods which generated greenhouse gases in their production)."

If you do the math, this estimate assumes per capita emissions of 4.33 tons of CO₂ for each of those 300 million people whose births were avoided, which is a number consistent with the World Bank's estimate of China's per capita emissions in 2005. Although the The Economist article by no way says this, the implication is that the world is better off with 300 million fewer Chinese.

However, one offensive example deserves another. Had we arrested population growth in the US over the same period, 1970 - 2005, there would have been 95 million fewer Americans in the world. Using the per capita emissions of the US in 2005 - 19.7 tons per person - would have prevented 1.9 billion tons of CO₂. This is 1.5 times as much GHGs as that avoided by the Chinese!

One take-home message could be that more would have been accomplished by reducing the number of Americans than Chinese. Maybe America needs a 1-child policy - or the oppressive government that such a policy would require. The last is meant sarcastically.

As far as I can tell, no one is seriously offering population control as an explicit climate change mitigation policy. Nevertheless, I think the issue of population growth and its environmental implications is something worth highlighting. Indeed, fear about overpopulation is a perennial worry. There are legitimate concerns about population growth, but these are mostly to do with its relationship to the rights and status of women and local issues of economic development.  The assumption that population growth is a leading cause of global environmental degradation is really problematic because it misses (or deliberately hides) the radical inequalities in consumption between different populations. Some births have more environmental consequences than others.

It is frequently pointed out that China and India are the most populous countries on the planet (1.4 and 1.3 billion, respectively), but it is not often pointed out that the US is the third most populous country on the planet (319 million). But what's more important, from an environmental perspective, is the relative impact of these populations, not their sizes.

Consider the impact if America reduced its per capita emissions to levels similar to China, or better yet, India.

• In 2010, American emissions of CO₂ were 17.1 tons per capita, while in China they were 6.2 tons per capita, and in India, 1.7 tons per capita.
• Each American, on average, emitted CO₂ equivalent to 2.75 Chinese or 10 Indians.
• If America reduced its per capita emissions to levels similar to that of China (holding Indian emissions steady), there would be roughly 3.5 billion tons less of CO₂ in the world annually. If we treated this 3.5 billion tons of avoided CO₂ as "room" for other people to exist, this would be equivalent to making room for another 500 million Chinese, or another 2 billion Indians! 
• If the US reduced its per capita emissions to that of India (holding Chinese emissions steady), there would be "room" for another 790 million Chinese or 2.9 billion Indians!

This idea of "making room" for other people is not so radical as it might sound. Indeed, "making room" is implicitly what arguments about population growth are often really about, at least when invoked in the context of global environmental problems. But the question is: making room for who and for what?  For wealthy countries to continue a particular way of life with its high environmental impact? For poor countries to develop economically and reduce mass poverty? 

This question touches on a core debate that has plagued climate change negotiations since the 1990s; how to fairly allocate responsibility for climate change mitigation, especially between more developed and less developed countries. A large part of the problem is that consumption (as in per capita emissions of CO₂) is still a reliable proxy for wealth. Wealthier countries (and individuals) consume more (emit more CO₂ per capita) than less wealthy countries (and individuals). So long as this relationship between wealth/development and consumption hold, we have an environmental and a moral dilemma. This is the core challenge.