A little over two centuries ago, in the year 1800, roughly a billion people called Earth home.
Just a century later, it had grown by another 600 million.
Today, there are around 8 billion people on the planet.
That sort of growth is unsustainable for our ecosphere, risking a 'population correction' that according to a new study could occur before the century is out.
The prediction is the work of population ecologist William Rees from the University of British Columbia in Canada. He argues that we're using up Earth's resources at an unsustainable rate, and that our natural tendencies as humans make it difficult for us to correct this "advanced ecological overshoot".
The result could be some kind of civilizational collapse that 'corrects' the world's population, Rees says – one that could happen before the end of the century in a worst-case scenario.
In such an event, even the richest societies would be completely vulnerable, Rees estimates.
"Homo sapiens has evolved to reproduce exponentially, expand geographically, and consume all available resources," Rees writes in his published paper.
"For most of humanity's evolutionary history, such expansionist tendencies have been countered by negative feedback. However, the scientific revolution and the use of fossil fuels reduced many forms of negative feedback, enabling us to realize our full potential for exponential growth."
Rees points out our dominance over the planet has made us forget that we are still governed by natural selection. What's more, our natural inclination towards short-term thinking, which served us exceedingly well in our evolutionary past, continues to compel us to take as much as we can possibly get when it's available.
This has fueled the excessive consumption and pollution that a portion of the current world population is now responsible for, which is set to increase as financial security and population sizes increase, Rees argues.
A changing climate is evidence of the strain the planet is already under but it's only a tiny fraction of the overall problem of overshoot, Rees argues.
As Rees points out, as we continue to use an abundance of fossil fuels we're simultaneously ignoring the other symptoms of overshoot too. From our consumption of biomass to the disruption of planetary nutrient cycles, these interlinked problems are all propelling Earth's sixth mass extinction and risking a chaotic break-down of our planet's essential life-support systems.
What's more, our proposed solutions, such as switching to renewables don't actually address the problem of exponential population growth and in fact further contribute to the excess consumption that goes along with it.
The question is whether improvements in technology – in everything from combating climate change to increasing food production – are capable of keeping pace with the growing demands our consumption places on the planet.
If innovation can't provide solutions, food shortages, habitat instability, war, and disease may well start to make an impact in population numbers, this study predicts.
"While no major symptom of overshoot can be adequately addressed in isolation from the others, addressing overshoot directly would reduce all important symptoms simultaneously," Rees explains.
Another point that Rees makes – and he's not the first to do so – is that we need to be much more aware of the peril that we're in, and should be working out ways to get a better balance between our give-and-take relationship with the planet.
"In the best of all possible worlds, the whole transition might actually be managed in ways that prevent unnecessary suffering of millions (billions?) of people, but this is not happening – and cannot happen – in a world blind to its own predicament," writes Rees.
The research has been published in World.