There is no quick fix for the 'population time-bomb' and even a world-wide one-child policy like China's or catastrophic mortality events may still result in 5-10 billion people by 2100, according to a new study.
Ecologists say that the "virtually locked-in" population growth means the world must focus on policies and technologies that reverse rising consumption of natural resources and enhance recycling, for more immediate sustainability gains.
Fertility reduction efforts, however, through increased family-planning assistance and education, should still be pursued, as this will lead to hundreds of millions fewer people to feed by mid-century, researchers said.
"Global population has risen so fast over the past century that roughly 14 per cent of all the human beings that have ever existed are still alive today - that's a sobering statistic," said Professor Corey Bradshaw from the University of Adelaide's Environment Institute.
"This is considered unsustainable for a range of reasons, not least being able to feed everyone as well as the impact on the climate and environment," said Bradshaw.
Researchers 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," said Bradshaw.
The researchers constructed nine different scenarios for continuing population ranging from "business as usual" through various fertility reductions, to highly unlikely broad-scale catastrophes resulting in billions of deaths.
"We were surprised 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," said Professor Barry Brook, Chair of Climate Change at the Environment Institute for the study.
"Yet, as our models show clearly, while there needs 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," said Brook, now Professor of Environmental Sustainability at the University of Tasmania.
"The corollary of these findings is that society's efforts towards sustainability would be directed more productively towards reducing our impact as much as possible through technological and social innovation," Bradshaw added.
The study was published in the journal PNAS.
