Climate Feedback

Population: elephant in the greenhouse?

<img alt=“climate.2008.44-i1” src=“http://www.nature.com/climate/2008/0806/images/climate.2008.44-i1.jpg” align=“right” hspace=“10px”/ /> In debates over how to mitigate the effects of climate change, is the burgeoning human population an elephant in the room? A projected 9 billion people will have to share a warming planet by 2050, yet as Kerri Smith writes in Nature Reports Climate Change this week, the climatic effects of their rising numbers and shifting demographics has received surprisingly little study.

Population is a touchy subject, bringing to mind oppressive campaigns against growth – like China’s one-child system, or forced sterilization programs – as well as false past predictions of an imminent catastrophe. But it’s becoming clear that the problem is more complex than a ticking ‘population bomb’. Numbers are exploding in the world’s poorest societies – a trend that CIA chief Michael V. Hayden recently chose above climate or energy issues as one of the key changes facing the 21st century. Because of the low emissions per head in these societies, Smith explains,

Reducing population growth in Niger, for example, where the population size is predicted to triple by mid-century, would not have a dramatic effect on emissions right now. And in many countries in Europe — where reducing emissions levels is more pressing — populations are declining, so a demography-based climate strategy would be ineffective. In a generation’s time, however, when developing countries begin industrializing apace, a large population could be bad news.

An aging industrialized world could wrinkle the picture further, as could increasing urbanization. Meanwhile, Hayden fears that the population patterns themselves will precipitate political instability – which climate change is expected to exacerbate.

The solutions to this complex problem could be subtle, or at least subtler than enforcing a small average family size. Fred Meyerson, an ecologist, demographer and environmental policy researcher, told Smith that simply improving access to family planning in the last 50 years has very effectively reduced population growth, and the UN Population Division’s Thomas Buettner pointed out the knock-on effect that this has had on greenhouse gas emissions. (A new book by the WorldWatch Institute’s Robert Engelman puts a finer point on it, arguing that in countries where empowerment of women gives them say over the matter, they invariably choose to have two children or fewer on average.)

And this month’s headlines show how far-reaching the links are between slowing population growth and preventing climate-induced crises, Meyerson added in an email:

Each million/billion [people] we add puts more people in the path of natural disasters such as the recent Asian cyclone and drought/starvation, some of which are climate change-induced. Adaptation to those changing conditions (including migration, if needed) is obviously much more manageable with 8 rather 11 billion people. And emissions mitigation – for instance, a move from fossil fuels to biofuels – is also much more problematic if the lion’s share of the solar energy budget of the terrestrial surface is needed to meet the food needs of a large population and not available for energy production. (That debate is already ongoing with the spike of food prices and the use of corn for ethanol production, but it will surely increase as we add ~75 million people each year to the population over the next few decades.)

Anna Barnett

Photo: Lusi, SXC

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    JohnLopresti said:

    Besides the post’s appropriate linkage of populations’ ways of solving overcrowding, there is another ill-boding feedback mechanism engaged ever more tightly by overpopulated societies, namely, the centrifugal impetus of individual achievers to become like their firstworld counterparts where per capita net influence toward escalation of global warming is most pronounced, that is to say, deprived people want the luxuries and will generate global warming as a means to achieving those aspirations. Hayden is appropriate with respect to security risks but misses the important feedback linkage, perhaps mostly because it might appear impolitic to discuss just now.

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