Prof Harper is thrilled about recent declines in fertility:

Prof Harper told the Telegraph: "I think it's a good thing that the high-income, high-consuming countries of the world are reducing the number of children that they're having. I'm quite positive about that."

The academic said declining fertility in rich countries would help to address the "general overconsumption that we have at the moment", which has a negative impact on the planet.

Most importantly, declines in births will bring about reductions in CO2 emissions from wealthy nations, Prof Harper points out:

Research has found that wealthy nations tend to have much larger carbon footprints than poorer countries, as rich people can afford to buy more goods, travel more and do other activities that generate emissions.