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C02 emissions and fertility rates

Finally, a short break. I have been working on my main topic, the nexus of energy and development. And eventually of course the implications for the surplus approach. As part of a recent department environmental sustainability seminar centering on the models of Armon Rezai (and Lance Taylor and Duncan Foley), I presented data and (gasp!) forecasts using the Kaya model of carbon intensity. Surprisingly, there is hope in the data.

One of the points that leapt from the data is that population dynamics are a far greater weight on carbon emissions than the greening of the energy supply ("carbon intensity") and efficiency of energy consumption ("energy intensity"). Respectively, population is seven and three times more important in carbon emissions than either of those.

So, fertility becomes an (the?) important issue in climate debates. The data on global GDP per capita growth are among the most stable, and therefore predictable, that I have seen in macroeconomic series. In one hundred years, each of us will be earning $70,000 in 2005 USD (up from $7,000). Every one of us. Place your bets. So how many will that be?

The great news is that global fertility levels are plummeting, headed toward population decreases. One can see that in this Hans Rosling inspired motion chart using mainly World Bank data (with a recent addition of Jamie Galbraith's world inequality data based on Henri Theil indices). For those who may be concerned, I have no data on global coitus rates; I presume they remain healthy.

The data indicate that per capita GDP increases, female education, and more equal income distribution correlate with reduced fertility. This is great news since the first two are clearly "in train" around the world based on the data. Distribution, the great economic problem, jeopardizes climate as it becomes less equal in major economies.

Note that China has a current fertility rate of 1.6, below the 2.1 population sustainability rate. The biggest surprise is India, whose fertility at 2.7 was achieved without autarchy, a powerful endorsement of economic progress in damping fertility rates.

So we can have growth with some hope for climate given declining fertility rates even at current projected levels of carbon and energy intensities. My data intensive slides are here (including a discussion of the Kaya model). I gladly take questions. I will defer policy proposals. I need to refine the idea of global Fed helicopter drops of family planning supplies. (the interrupter of last resort?)

In a future post, with some trepidation, I will investigate the possibility of radical energy regimes and their implications for our economic and respiratory future. Are we approaching the end of the fossil energy epoch? An incredibly interesting question.


  1. Two points that you may want to emphasize. First, in Keynesian fashion you are not arguing for less growth or degrowth (as do some green Marxists). Second, more radical improvement on the income distribution front would also be green. On a different point, I do have some episodical data on coitus, but would rather keep it private.

  2. Great points on which I fully agree. Further in the weeds of climate models lurk the mysteries of "damage functions" which modelers invoke to limit growth of output and emissions.

    We may have instead a natural limiter, reduced fertility, which of course is not a damage function. A far more hopeful story. At this rate, I may never be awarded my Carlyle credentials.


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