Quora: Is Overpopulation Causing Global Warming?

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Carbon dioxide pulled from the air could satisfy a $1 trillion unmet market demand. Jim Urquhar/Reuters

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Answer from Michael Barnard, low-carbon innovation analyst:

Global responses to overpopulation started decades ago. Global responses to global warming and attendant climate change arrived much later. There is a relationship, but they are not the same things.

First off, overpopulation has been identified multiple times throughout history as a concern, with perhaps three key times standing out in my memory.

In 1798, Thomas Malthus, an English scholar and minister, published an assessment of population growth versus the ability to feed more people. He identified that in the absence of significant ongoing innovation, the population of the Earth would exceed humanity’s ability to feed itself. Every time we improved our ability to feed more people, more people would then get born in a never ending cycle which would eventually collapse. Except for regional famines, we’ve managed to keep ahead of that collapse.

In 1968, 170 years after Malthus, a Stanford professor named Ehrlich published an alarmist book called The Population Bomb foretelling a Malthusian catastrophe in the coming two decades. It received a lot of public attention and created at least partial political will to do something globally, although that took time.

In 1983, Gro Brundtland was commissioned to develop a global perspective on achieving some balance between economic development, population and the environment. Her 1987 report clearly identified that richer countries stopped having lots of babies and making poor countries wealthy was a key mechanism to stopping Malthusian growth curves. At a certain level of wealth and ability to feed our excess population, we stop increasing. This doesn’t mean we stop increasing our consumption per capita however, which is a different issue.

This focus on bringing people out of poverty along with amazing efforts in giving women education and control over their fertility in high-fertility regions has led to a significant reduction in the rate of population increase. Right now, it looks as if around 2100 we’ll stabilize.

Japan might be ahead of the curve here as the population is actually declining. They aren’t accepting immigrants and their fertility is well below replacement. This is a vision of a future world where countries like Canada can’t depend on the ‘teeming masses’ of poor countries wanting to immigrate. This can be seen already between the USA and Mexico. Ignoring the current political rhetoric, net flows of people have been going into Mexico for the past decade, not into the USA.

People will still move around, but much less because they are from deeply impoverished countries with too many other people.

Which brings us to global warming.

About the same time as Malthus, the Industrial Revolution was starting up. Watt’s improvements on the steam engine in 1781 led to massive increases in power available to industry. And lots more coal being burned. In 1861, Siemens built the first coal generator of electricity which led to massive increases in much more fungible electricity. And lots more coal being burned.

In 1885 Benz developed the internal combustion, gasoline powered car. Then in 1908, Ford brought it to the masses. Lots of oil being burned.

Coal, oil and other fossil fuels have the defining characteristic that when they are burned, the carbon in them combines with oxygen from the atmosphere in a 1–2 ratio forming carbon dioxide. That gas traps infrared radiation emitted by the earth after the sun’s rays hits it better than a lot of other gases.

All of that coal and oil led to global warming. This wasn’t exactly a surprise. It was first predicted in 1899 based on the work of various scientists studying atmospheric composition and its effects. Arrhenius, Langley and Chamberlin tend to get mentioned, but it wasn’t exactly a tricky issue to figure out. Change the atmosphere with lots of CO2 and the temperature will change.

Population growth is not the direct cause of global warming, burning fossil fuels is.

Where some of the confusion comes from is that CO2 emissions are reasonably well correlated to population.

It’s not a one-to-one relationship, but there is a solid relationship. For a couple of centuries, more people meant a great deal more CO2 which more closely tracked gross domestic product on a one-to-one ratio. As countries became richer, that was reflected in their GDP and also in their reduction in fertility. More GDP equals flattening population but still increasing CO2 emissions.

Until recently. The International Energy Agency tracks this sort of thing, and last year published this very hopeful report. CO2 emissions had flattened, but GDP growth has continued.

So now the global population is continuing to rise, but more slowly. The global GDP is continuing to rise. But global emissions of CO2 have flatlined.

There’s every indication that the relationship between population and global warming and GDP and global warming has been broken. And that continued penetration of wind and solar generation and electrification of transportation will fundamentally destroy the historical relationship.

That’s really good news.


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