In an op-ed for the New York Times, Professor Jared Diamond points to consumption differentials between rich and poor countries as the factor responsible for our global sustainability crisis. Diamond says we are running out of resources, and will do so all the faster as developing countries try to "catch up" with rich country consumption levels. While this is true, it is bewildering that Diamond dismisses population as a factor in the path toward global unsustainability, as well as potentially a policy lever for slowing our progression down that path.

Diamond says, "The population especially of the developing world is growing, and some people remain fixated on this. They note that populations of countries like Kenya are growing rapidly, and they say that's a big problem. Yes, it is a problem for Kenya's more than 30 million people, but it's not a burden on the whole world, because Kenyans consume so little."

He further says we should be concerned about what happens when Kenyans (and other developing world people) achieve developed country consumption levels, and all of us - rich and poor countries alike - should seek ways to improve quality of life with sustainable consumption levels. Population does not get another mention.

Pointing to high consumption as the cause of unsustainability without also addressing population is like saying that only SUVs cause road congestion! In that case, there should be no reason for concern in India about traffic jams (and emissions) from the new 1 lakh Tata Motors car.

Of course, as with traffic congestion, numbers of people do matter, as does size. And we won't come close to solving global warming, or broader issues of resource sustainability, if we don't address both numbers of people and consumption levels.

The number of people in the world (and their distribution and ages) affect overall consumption directly; and through a variety of indirect channels, affect other economic outcomes that have a bearing on sustainability. This includes GDP (with links to population through labor supply, savings, and human capital investment) and its distribution. It is population's effect on these variables, and how to achieve desired levels of population growth at the micro level (reducing unwanted births) and the macro level (realizing demographic dividends) that we must understand better and communicate to professors and policymakers alike.

In their 2001 volume, Birdsall, Sinding, and Kelley offer convincing but not well-known evidence that slower population growth does improve economic outcomes. More recently, new research is being supported by the William and Flora Hewlett Foundation aimed at deepening our understanding of how population affects economic outcomes by using new analytical methods that help overcome data deficiencies and new and expanded datasets that invite the application of new methods. The research is focused on Africa.

In partnership with the Institute of International Education, the Hewlett Foundation is inviting applications from Ph.D. students based in the U.S., Canada, and Africa for fellowships to support their work on population and economic linkages. The deadline for applications is April 1, 2008 (for U.S. applicants). The two-year-old fellowship program has already engaged some of the best and brightest Ph.D. students in economics and other social sciences to help us understand how population policies can be part of the solution to the sustainability problem.