Human population continues to grow by more than 75 million people annually. Since the first
Earth Day in 1970, global population and annual carbon dioxide emissions have both increased by
about 70 percent. As a result,
capita emission rates remain steady at about 1.2 metric tons (mt) of carbon per person per
Unfortunately, the 1997 Kyoto Protocol has had little measurable effect on per capita emissions,
even in the countries that have agreed to national targets. Emissions in Western Europe reached 2
mt per person back in 1970 and have fluctuated just above that level ever since. The same plateau
phenomenon, which appears to be related to stages in development,
happened in the early
1970s in “centrally planned Europe,” which includes Russia and the former Soviet republics.
Per capita carbon emissions in the United States also leveled off around 1970 at a much higher
rate–above 5.5 mt per person–and have barely budged since, through recessions, economic booms,
and swings in energy markets. From 1970 to 2004, U.S. population and emissions both rose by 43
More than any another factor, population growth drives rising carbon emissions, and the U.S.
Census Bureau and United Nations both project that global population, currently 6.6 billion, will
surpass 9 billion before 2050.
It is, of course, possible that per capita emissions could decrease in the future, but a number
of factors make this difficult. First, emission patterns are “sticky” due to slow turnover in our
energy-intensive infrastructure, including power plants, housing, and vehicle fleets. Established
consumption behavior is hard to change, by either individuals or nations.
Second, while global per capita emissions have been relatively flat for decades, there is now
more risk that they will rise, not fall, in the near future. Coal (which releases the most carbon
per unit of energy when burned) is more abundant and less constrained than petroleum and gas. As
oil becomes scarce and expensive, and population growth and development drive up energy demand,
coal use has
grown dramatically in recent
years, particularly in China, but also in the United States and India.
Finally, many developing countries that are experiencing explosive economic growth have not yet
reached per capita emissions plateaus and also have rapidly rising populations. All these factors
more than wipe out the minor savings associated with my family (and others) switching to compact
fluorescent bulbs and efficient front-loading washers.
The implication is that one of the best strategies for reducing future greenhouse gas emissions
is population stabilization, as quickly as can be achieved by non-coercive means.
But is stabilization likely or possible? The United Nations projects that global population will
eventually peak well above 9 billion, based on the assumption that fertility rates in every country
on the planet will converge at 1.85 children per woman (below the 2.1 replacement fertility level),
and that most countries will achieve this target, or close to it, by 2050. This critical
assumption, adopted relatively recently by demographers, is based only on a mathematical formula,
and perhaps some wishful thinking. It is quite possible that global population could surge well
beyond even current projections.
Unfortunately, given our current trajectory, the disruptions, hardship, and conflict caused by
climate change and variability may well increase death rates (and decrease life expectancy) before
declining fertility stabilizes population.
So, I believe the best course of action for both human well-being and climate policy is to
quickly devote as many resources as possible to reducing unwanted pregnancy, so that we reach
half of all
pregnancies in the United States, and one-third globally, are unintended. We can do better than
that, and several countries
This will require rehabilitation of the population policy and family planning fields, which have
been attacked, shunned, and splintered in recent decades. Conservatives are often against sex
education, contraception, and abortion, and they like growth–both in population and the economy.
Liberals usually support individual human rights above all else and fear the “coercion” label, and
therefore avoid discussion of population policy and stabilization. The combination is a tragic
stalemate that leads to more population growth. We need to get over it.
And certainly population policy should be front and center at the
U.N. Framework Convention on Climate Change
meeting, which begins today in Bali.
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