What if... the world had a one-child policy?

I recently received a request to look at the emissions impact of sterilizing everyone on the planet. Good idea, I thought... But I'm not too keen on suggesting we implement the demise of the human species. So I thought I'd go for something a little less dramatic. In 1978 China's government introduced a one-child policy to tackle issues of overpopulation. What would be the impact on greenhouse gas emissions if the rest of the world were to follow suit?

There's lots of reasons to be worried about overpopulation. More people consume more stuff. And on a finite planet with limited resources, if the population increases too far - there might not be enough 'stuff' to go round. The video below sums it up nicely. But since this is a blog about climate change I'm going to look purely at greenhouse gas emissions.

I was surprised to find that globally, per capita emissions haven't changed much in the past 60 years. But total greenhouse gas emissions have seen an exponential upward trend. It follows then that the increase in emissions must be down to more people. This was certainly the conclusions drawn by a group of Washington based researchers who identified population size and affluence as the key drivers of human environmental impact.

Concerns such as this spurred the formation of the Optimum Population Trust, a group committed to curbing world population increase, in 1991. Today they count David Attenborough, James Lovelock and Jonathon Porritt amongst their members. They run a campaign which allows people to offset their carbon emissions by paying for contraception in developing countries. Increase access to contraception, they claim, and reduce the population expansion that is driving emissions. But will it work?

It turns out that the relationship between population size and emissions isn't quite so straightforward. Take Uganda for instance, a country with one of the highest birth rates in the world. The average person in Uganda is responsible for roughly 70 times less carbon emissions than a person in the UK. So even if the population of Uganda increases ten fold, the overall effect on global carbon emissions will be tiny. This pattern can be seen all over the developing world where rapidly increasing populations will result in little impact on emissions.

Far more important to emissions than population size, is population demographics. This paper by Michigan State University estimated that China's one-child policy had reduced births by 300 million by 2005. But this had been largely offset by an additional 80 million households brought about by increased divorce rates and children leaving home earlier. More homes consume more energy resulting in more emissions.  You might also want to look at age. Although here the outcome is less obvious. Some studies point towards people of a working age having a higher carbon footprint, others suggest that older people do.

So the idea of simply reducing population may not have such an obvious impact on emissions right now. A one-child policy might work to reduce emission in the UK, where our per capita emissions are large. But it won't make an immediate impact in the developing countries where populations are growing at their fastest. However if these countries develop in a similar fashion to the UK in the future, expanding their per capita emissions, population policies introduced now could play a vital role.

And if you don't like the thought of a Chinese style forced family planning regime, take solace in this report by the UN Population fund. They found that by far the most effective way of reducing birth rates in developing countries is to empower women, giving them the choice of when, and if, to have children. It's cheap, increases women's education rates and encourages them to play a more active role in society. I think you'd be hard pressed to find someone who didn't agree with that!