Scientists have found that even stern restrictions over fertility or a catastrophic event would not be able to reduce the world population.
Ecologists Professor Corey Bradshaw and Professor Barry Brook from the University of Adelaide's Environment Institute said that the "virtually locked-in" population growth meant the world must focus on policies and technologies that reverse rising consumption of natural resources and enhance recycling, for more immediate sustainability gains.
Professor Bradshaw said that the global population had risen so fast over the past century that roughly 14 percent of all the human beings that had ever existed were still alive today. This was unsustainable for a range of reasons, not least being able to feed everyone as well as the impact on the climate and environment.
They examined various scenarios for global human population change to the year 2100 by adjusting fertility and mortality rates to determine the plausible range of population sizes at the end of this century. Even a world-wide one-child policy like China's, implemented over the coming century, or catastrophic mortality events like global conflict or a disease pandemic, would still likely result in 5-10 billion people by 2100, he said.
Professor Brook added that a five-year WWIII scenario mimicking the same proportion of people killed in the First and Second World Wars combined, barely registered a blip on the human population trajectory this century.
Their models show clearly, while there was a need to be more policy discussion on this issue, the current inexorable momentum of the global human population precludes any demographic "quick fixes" to our sustainability problems.
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The study revealed that effective family planning and reproduction education worldwide have great potential to constrain the size of the human population and alleviate pressure on resource availability over the longer term.
The findings are published in the Proceedings of the National Academy of Sciences of the USA.