Climate change has taken global centre stage in recent months following three reports by the Intergovernmental Panel on Climate Change that paint a dire picture of the future should governments fail to take action on reducing greenhouse gas emissions.

But when the discussion turns to modifying our behaviours in order to reduce CO2 emissions in order to keep the planet from warming 1.5 C or 2 C above pre-industrial levels, the threshold that would result in widespread damage, one word creeps up more often than not: overpopulation.

The argument is that if there were fewer people on Earth, greenhouse gases would be reduced and climate change could be averted. But experts say population control isn't the panacea some think it might be.

"It is a very complicated, multifaceted relationship. Population issues certainly are an important dimension of how society will unfold, how society will be able to cope with this crisis over the course of this century," said Kathleen Mogelgaard, a consultant on population dynamics and climate change and an adjunct professor at the University of Maryland.

"But it's not a silver bullet, and it's certainly not the main cause of climate change. And fully addressing population growth is not, on its own, going to be able to solve the climate crisis. But it is an important piece of the puzzle."

It took 123 years for Earth to go from 1 billion to 2 billion people. The gap has progressively narrowed, to just over a decade to reach the next billion.

Robert Engelman, a senior fellow at The Population Institute in Washington, D.C., agrees that battling climate change isn't just about slowing population growth.

"Is population an issue in climate change? Absolutely. Is it underreported, underrated, under-talked-about as an issue in climate change? Absolutely," Engelman said. "If it were just Adam and Eve on the planet, they could fly a 747 around the world 24/7 and heat Mar-a-Lago and 25 other homes with coal, and it wouldn't make a difference."

But he notes slowing population growth alone "won't solve" climate change.

"It's one of a number of things that needs to be considered as we try to address or respond to this incredibly difficult problem that the world is facing. There's no one thing that's going to do it."

Declining birth rates

The reality is global birth rates are declining.

The United Nations had previously projected that the global population would reach 11.2 billion by 2100. However, the UN updated that forecast in June — dropping it to 10.9 billion.

That's because fertility rates are dropping for most of the world.

Darrell Bricker, a fellow at the University of Toronto's Munk School of Global Affairs and Public Policy, who co-wrote Empty Planet: The Shock of Global Population Decline, says he's not surprised by the UN dropping its numbers.

"What's happening in most countries around the world is that the fertility rates are collapsing more quickly than the UN is estimating in countries that have above replacement rate fertility," said Bricker.

The replacement rate, or total fertility rate, is the number of births it takes to keep a population from either increasing or decreasing. It's roughly 2.1.

But that number isn't being reached in many parts of the world. So instead of the population continuously increasing, Bricker believes it will peak around the middle of the century — at around eight or nine billion people — and then begin to decline.

China is home to nearly 1.4 billion people. It's estimated that India could soon surpass that number. (Jason Lee/Reuters)

Another big driver for the decline in population is urbanization, Bricker says. In the 1960s, roughly 33 per cent of the population lived in a city; now it's 54 per cent. The UN projects that by 2050, that number will climb to 68 per cent .

"We're going through the biggest migration in human history right now, and that's people moving from the country to the city," Bricker said.

And when people move to the city, they tend to have fewer children.

'Draconian pledge'

The apocalyptic vision of overpopulation has been "imprinted in our brains" for so long, Bricker says, that it's often a knee-jerk reaction to call for population control.

Concern about overpopulation has been rather long-standing. One of the most familiar arguments, by Thomas Robert Malthus, dates back to 1798. In An Essay on the Principle of Population, Malthus wrote that population growth would eventually surpass our ability to provide sustenance for the masses — a belief now known as Malthusianism.

The fear of overpopulation has even seeped into our pop culture: In the recent Marvel movies Avengers: Infinity War, the villain, Thanos, wants to eliminate half of the universe's population in order to end suffering , such as starvation.

But Bricker believes it's gone too far.

He's particularly irked by recent stories about youth pledging not to have children; while many talk of fears over what the world will look like in the generations to come, still others point to population concerns.

The birth rate in Canada is 1.5, he notes, below the replacement rate.

"So why are you taking this pledge? If you decide you want to have a kid, great. If you decide you want to have two kids, great," he said.

"There are a lot of reasons why we should be concerned about global warming and climate change. And, yes, we need to do whatever we need to do to control it. But if you think you need to enforce some sort of Draconian pledge on people to say that they shouldn't have a family or whatever, you're just missing the point."

Though the global population has been rising steadily, birth rates are declining in many parts of the world. (Teresa Crawford/The Associated Press)

China's one-child policy was introduced in 1979, but lifted in 2015. Interestingly, their birth rate didn't climb after the end of that policy; it has remained steady at roughly 1.7.

The other thing to take into consideration about our growing population is that the issue isn't so much about births, but rather about dying. Or more accurately not dying. Today, people are living longer.

In China, for example, the average person lived to age 40 in 1950, Bricker said. According to the World Bank, the country's average life expectancy is now 76.5 , and by the mid-2030s, the average person should live to 80.

Access and education

One of the universal calls to prevent the global population from ballooning is to better educate women , particularly in developing countries.

"The key to achieving slower population growth is best done through a rights-based approach that includes educating girls and providing universal access to family planning and reproductive health services," said Mogelgaard. "That is the best and most sustainable way to achieve reductions in fertility that leads to slower population growth."

Eighteen Metro Vancouver centenarians came together on April 24, 2019, to celebrate centuries of milestones and memories. One thing to consider about our rising population is that people are living longer today. (Ben Nelms/CBC)

But she says it's important that family-planning choices are left up to the woman — and that's not the norm in many countries of the world, though global access to contraception has improved in recent decades.

"We are still seeing that there are hundreds of millions of women around the world who would like to be able to have greater control of their fertility, but don't have real meaningful access to the information and services that will allow them to do that," Mogelgaard said.

The issue of CO2 emissions

What's more, a larger population doesn't necessarily produce more CO2 emissions, at least, not on a per capita basis.

Michael Barnard, chief strategist with TFIE Strategy Inc. who specializes in energy and low-carbon solutions, points back to China as an example: While the country of 1.4 billion people is the No. 1 emitter of CO2 in the world, on a per capita basis, it produces far fewer emissions than either the U.S. (the world's second-top emitter) and Canada (the 10th).

According to a recently updated explainer by the Union of Concerned Scientists , the U.S.'s CO2 emissions from fuel combustion per capita is 15 tonnes, and Canada sits at 14.9 tonnes.

China? They're at just 6.4 tonnes per capita — a trend that is starting to drop.

That's also the case for India, Barnard said.

"Per capita is important," he said. "One-third of the population already have lower per capita CO2 emissions than we do, and they're dropping faster."

Instead of looking at population control as the biggest factor in the battle against climate change, experts say it's about looking at better education for women, adopting cleaner energy and changing our overall consumption patterns, especially in developed countries.

There is no single solution.

"Just because we slow population growth, if we continue to use coal-fired power plants to generate electricity, or if we continue to cut down forests at the rate that we're cutting down forests, those are going to be challenges regardless what the population is," said Mogelgaard.