The United Nations has published its latest projections for world population. It predicts that the current 7.3bn people on the planet will reach 8.5bn in 2030, and could be 11.2bn at the end of the century. India is expected to overtake China as the most populous country.

The annually updated forecasts are fuel for a strengthening argument that growing population is a critical environmental issue. The logic is simple: increasing numbers of people multiplied by higher average consumption from wood fuel to mobile phones and intensively farmed meat is a double whammy for the environment. The results are depleted raw materials and polluted soil, water and air. Greenhouse gas emissions causing climate change, specifically carbon dioxide, are the common measurement of this relationship. So persuasive is the strand of thought that it has attracted backing from respected public figures such as Sir David Attenborough, Jonathon Porritt and Chris Packham. But it is flawed.

If expanding population is a problem, campaigners on the subject advocate action to slow and stop the rise, if not reverse it. (The UK group Population Matters, for example, says it is “responsible” to have one or two children – below the replacement rate at which population would be stable.) This presents challenges. The first is that much of the rise in population is due to people living longer. Nobody is credibly suggesting that society should cease trying to find cures for disease or stop stepping into disaster zones to save lives.

Any reduction in population rates, therefore, falls on women having fewer children. This has happened – average fertility has been falling for years, even in Africa, which continues to have the highest number of children per woman. But the second challenge for population campaigners is that biodiversity loss and pollution continue apace.

The fact is that it is in the very poorest countries where women have the most children, on average. And where population growth slows, generally economic growth speeds up, and carbon emissions rise faster. This happens on a global scale and even within countries – certainly within the poorer ones where there is most scope for population control, and where, also, the potential for industrialisation is greatest. It is unclear which is cause and which is effect: it is likely that they play off each other. And in some cases, perhaps, population policies go hand in hand with economic reforms. Only in the wealthiest countries, though, which already have lower fertility rates, are these links weakened or even broken.

This phenomenon raises the counterintuitive possibility that curbing population growth could generate higher global emissions than would otherwise be the case. There are good reasons for addressing birth rates: empowerment of women is a major one. And education, birth control clinics and popular soap operas in Brazil and radio programmes in Africa have all been successfully used to this end. But as an environmental policy, reducing the number of people is questionable. It provides a convenient distraction for richer nations with lower birthrates from the pressing need to reduce or decarbonise consumption. Worse, focusing on population growth could actually accelerate the global environmental problem it claims to address.