According to this study, neither another world war, a global pandemic, or a universal one-child policy will do anything to stop runaway population growth thanks to demographic momentum.
Apparently nothing can stop humanity from behaving like yeast:
According to the study, attempts to curb our population as a short-term fix will not work. If China's much criticised one-child policy was implemented worldwide, the Earth's population in 2100 would still be between five and 10 billion, it says.Population controls 'will not solve environment issues' (BBC)
"We've gone past the point where we can do it easily, just by the sheer magnitude of the population, what we call the demographic momentum. We just can't stop it fast enough," said Prof Corey Bradshaw from the University of Adelaide. "Even draconian measures for fertility control still won't arrest that growth rate - we're talking century-scale reductions rather than decadal scale, because of the magnitude."
In their paper, the researchers also look at the impact on numbers of a global catastrophe in the middle of this century. They found that even an event that wiped out two billion people would still leave about eight and a half billion in 2100. "Even if we had a third world war in the middle of this century, you would barely make a dent in the trajectory over the next 100 years," said Prof Bradshaw, something he described as "sobering".
The pace of population growth is so quick that even draconian restrictions of childbirth, pandemics or a third world war would still leave the world with too many people for the planet to sustain, according to a study.Global overpopulation would ‘withstand war, disasters and disease’ (Guardian)
Rather than reducing the number of people, cutting the consumption of natural resources and enhanced recycling would have a better chance of achieving effective sustainability gains in the next 85 years, said the report published in the proceedings of the National Academy of Sciences.
“We were surprised that a five-year WW3 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 Prof Barry Brook, who co-led the study at the University of Adelaide, in Australia.
The second world war claimed between 50 million and 85 million military and civilian lives, according to different estimates, making it the most lethal conflict, by absolute numbers, in human history. More than 37 million people are thought to have died in the first world war.
Using a computer model based on demographic data from the World Health Organisation and the US Census Bureau, the researchers investigated different population reduction scenarios. They found that under current conditions of fertility, mortality and mother’s average age at first childbirth, global population was likely to grow from 7 billion in 2013 to 10.4 billion by 2100.
Climate change, war, reduced mortality and fertility, and increased maternal age altered this prediction only slightly. A devastating global pandemic that killed 2 billion people was only projected to reduce population size to 8.4 billion, while 6 billion deaths brought it down to 5.1 billion.
“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. 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 co-author Prof Corey Bradshaw, also from the University of Adelaide.
In other words, we're f*cked.