To bring climate change under control, humans have to make big changes to arguably the most basic human act: having babies.

That’s the upshot of a recommendation to control population growth, backed by more than 11,000 scientists from 153 countries. The recommendation is one of six outlined in a new study on ways to curb climate change. The statement declares a climate emergency and outlines policy strategies to mitigate the effects of climate change.

The full list of recommendations target six factors that influence the climate: energy, diet, economy, production of short-lived pollutants, natural ecosystems, and — controversially — human population.

The researchers don’t put an exact number on just how many babies would be acceptable. But they do say that the number of babies born across the globe would need to stabilize or reduce from the current rate. The researchers peg that at 200,000 births per day, but United Nations data suggests it is higher — that some 360,000 babies are born throughout the world per day.

William Ripple, lead author of the statement and professor at Oregon State University, brought together the thousands of scientists who signed the call to action. Reducing the global population must be part of the solution, the researchers say.

“It has grown dramatically and it’s a well-known fact that this trend is putting enormous pressure on the biosphere and the ecosystems and the climate,” Ripple tells Inverse.

Focus on birth control

To tackle the problem, birth control and sex education need to become more widely available to people around the world. And while birth control programs would be voluntary, improving education for young people, especially women and girls, would be a “win-win,” says Ripple.

“That’s been shown to have a major effect on fertility rates and also a major effect on human well-being,” he says.

To get climate change under control, humans may need to take dramatic action in their personal lives. blvdone / Shutterstock

Population is tied to resource consumption, Ripple says, and both are major factors in greenhouse gas emissions.

"Concerned people could voluntarily choose a smaller family size.

“Today, especially in developed countries, consumption is extremely high, and that is a major contributor to greenhouse gases,” he says. “Concerned people could voluntarily choose a smaller family size.”

Those who have the opportunity to reduce their carbon footprint by eating less meat, for instance, may also consider having one fewer child, Ripple says. It’s important to remember that developed nations consume far more resources — and emit far more greenhouse gases — than people in developing countries, he adds.

It’s clear that developed countries should carry most of the burden when it comes to climate change mitigation and adaptation, since those countries have historically emitted the most greenhouse gases, Ripple says.

“Social justice, in my view, would be a very important part of any discussion on population policy. It’s really important to honor diversity and equity everywhere,” he tells Inverse.

“The problem of over-consumption is mostly happening in developed countries, and that needs attention,” he says. “That’s got to be part of the discussion.”

Ripple acknowledges that asking people to change their reproductive plans is among the more controversial ideas in the paper.

“But our goal here is to have that as part of the conversation,” Ripple says. “We want these things debated and talked about rather than just swept under the rug.”

Population warnings, then and now

Regulating the global population may sound drastic, but scientists have been warning for decades that the amount of people on Earth is simply unsustainable. In a 1992 report, the Union of Concerned Scientists warned “of what lies ahead” if humans don’t take drastic steps to mitigate climate change, including tackling population size and growth.

“Pressures resulting from unrestrained population growth put demands on the natural world that can overwhelm any efforts to achieve a sustainable future,” they said.

"The climate crisis has arrived and is accelerating faster than many scientists expected."

That was 27 years ago. Since then, the global population has increased by 40 percent, from 5.5 billion people to 7.7 billion.

But despite the obvious pressure, the Intergovernmental Panel on Climate Change, a United Nations body responsible for providing a scientific view of climate change and how to respond to it, is “largely silent about the potential for population policy to reduce risks from global warming,” argued John Bongaarts, vice president of non-profit Population Council, and University of Denver professor Brian O’Neill in an article published in the journal Science last year.

“Population-related policies — such as offering voluntary family planning services as well as improved education for women and girls — can have many of the desirable characteristics of climate response options,” the scientists argued. Those include climate mitigation and adaptation, as well as benefits to human well-being.

Given climate change’s urgency, greenhouse gas emission-limiting approaches like these deserve higher priority, Bongaarts tells Inverse.

“A successful policy would give all women in the world full control of their reproduction so they can freely decide when and how many children to have,” he says. “Unfortunately, we are still far from this goal, and, as a result, about half of all pregnancies in the world are unplanned.”

Increased access to contraception will be key to tackling this issue, says Bongaarts. Since unplanned pregnancies are common in both rich and poor countries, better access is needed everywhere, he says. But addressing climate change will require action across sectors.

Climate crisis heats up

The author’s of today’s declaration say they want to provide the right information for others to draw their own conclusions about climate change. “They tell an incredible story that has been going on for the last 40 years,” Ripple says.

Unfortunately, that story has “very little good news,” says Thomas Newsome, Ph.D., a co-author on the statement and lecturer at the University of Sydney.

“You don’t need to be an expert climate scientist to understand that the indicators we present paint a very bad picture about the state of the Earth,” Newsome tells Inverse. Much of the information presented in the emergency declaration isn’t new, but the effects of climate change “are now clearly visible and impacting the day to day lives of people,” he says.

“The climate crisis has arrived and is accelerating faster than many scientists expected. It is more severe than anticipated, threatening natural ecosystems and the fate of humanity.”

Recent attention to climate change across the globe is encouraging, he says. School strikes, climate lawsuits, government declarations of climate emergency, and Pope Francis’ call for climate action could all make a difference.

“There are still ways we can make changes. It’s not too late to act,” he says. “And if we do make changes, we should see the trajectory of our graphs change in a good way over the next 40 years.”

Ripple agrees, saying that recent climate efforts across society give him hope.

“Businesses, governments, schoolchildren, scientists, all acting in tandem to move the conversation and action toward mitigating climate change, is hopeful,” Ripple says.

“I think we’re at a social tipping point on taking action on climate change.”