The Carbon Cost of Human Reproduction

The human population is rarely discussed in the context of human-induced climate change. As I write this, on February 2, 2010 at noon Mountain Standard Time, the World population is estimated at 6,800,295,487 people (see figure above).

You can find the population at the U.S. Census Bureaus web site; check it as you start to read this post and then when you finish to get an idea of how rapidly the population is growing (

What is astounding is that in the next hour, about 8600 people will be added to Earth.  In the next year over 75 million will be added–about two “Californias” (see Table 1 below). That means that water and food and jobs, all the things that go into living in the 21st century, have to be created for all these people. And it is not just next year, it is each subsequent year. And, the numbers keep rising exponentially. In only 4 years we will have added 309 million people, another “United States”!

Time unit       Births      Deaths       Increase
Year       131,940,516   56,545,138    75,395,378
Month       10,995,043    4,712,095     6,282,948
Day            361,481      154,918       206,563
Hour            15,062        6,455         8,607
Minute             251          108           143
Second             4.2          1.8           2.4

Table 1. From U.S. Census Bureau (link above in text).

As we add people they use energy—directly and to produce all the extra food water and goods. Because energy is mostly derived from fossil fuels, release of carbon to the atmosphere increases. We can think of this as human’s “carbon legacy”. A few years ago, Paul Murtaugh and Michael Schlax from Oregon State University, published an article titled Reproduction and the carbon legacies of individuals (Global Environmental Change, Vol. 19, No. 14-20, doi: 10.1016/j.gloenvcha.2008.10.007). They found that “Under current conditions in the United States, for example, each child adds about 9441 metric tons of carbon dioxide to the carbon legacy of an average female, which is 5.7 times her lifetime emissions.” This and a report written by the London School of Economics are highlighted in an article in the Washington Post  (September 15, 2009:  The London report found that it is far cheaper to invest in preventing births than in supplying extra energy for extra people and is far cheaper than developing new solar or wind power ($7/ton vs. $51-$24/ton). This shows how closely linked population growth and energy use are.

Oh, and as I finish writing this post, I checked the Population Clock:

Over 10,000 people have been added to the world!


About climanova

I am an Emeritus Professor of Geoscience at the University of Montana, Missoula and and Independent Scientist-Consultant. My posts will examine the physical processes forming the foundation for life on Earth and examine the role humans play in modifying those processes.
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One Response to The Carbon Cost of Human Reproduction

  1. Chuck says:

    Each successive generation seems predestined to ignore the observations of Thomas Malthus, Paul Erlich, and now Johnnie Moore. We are a nation of problem solvers because we are a culture of problem creaters– no amount of careful, rational thought, and planning (oops ! I said it !), it seems, can supplant
    our collective arrogance as a species–we are, as Michael and Ellen Kaplan point out in their excellent new book by the same title , “Bozo Sapiens”

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