Australian researchers have modelled the likely trajectory of the human population under a number of different scenarios to see if we have any chance of living sustainably in the future.

The bad news is that even global one-child policies and pandemic diseases wouldn’t cut population numbers enough to sustain our way of life.

Curbing resources and population control are the only ways to provide a more secure future for humanity, they say.

Ecologists Corey Bradshaw and Barry Brook from the University of Adelaide’s Environment Institute say that population growth means the world must focus on policies and technologies which reverse rising consumption and enhance recycling.

Fertility reduction efforts, however, through increased family-planning assistance and education, should still be pursued because this will lead to hundreds of millions fewer people to feed by mid-century.

“Global population has risen so fast over the past century that roughly 14% of all the human beings that have ever existed are still alive today – that’s a sobering statistic,” says Professor Bradshaw.

Population growth over time, in millions. Wikimedia Commons

“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.”

The 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 events like global conflict or a disease pandemic, would still likely result in 5-10 billion people by 2100.

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 World War III 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,” says Professor Barry Brook, now Professor of Environmental Sustainability at the University of Tasmania.

“Often when I give public lectures about policies to address global change, someone will claim that we are ignoring the ‘elephant in the room’ of human population size.

“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.

“Our work reveals 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.

“Our great-great-great-great grandchildren might ultimately benefit from such planning, but people alive today will not.”