Bernie Sanders said birth control can help fight climate change. Here's why it's such a thorny issue.

Brian Snyder/Reuters

Sen. Bernie Sanders speaks at a campaign rally in Dover, New Hampshire, on September 1, 2019.

• Sen. Bernie Sanders touched on one of the thorniest issues in politics during a climate change town hall hosted by CNN on Wednesday night.
• Sanders suggested that improving access to birth control and increasing women's reproductive rights could help thwart climate change. 
• But discussions on curbing population growth tend to be associated with controversial topics such as eugenics. 
• With that said, there's a fair amount of research suggesting improving access to birth control could help slow global warming.
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Sen. Bernie Sanders on Wednesday suggested that empowering women across the world by offering improved access to birth control could help thwart climate change.  

During a climate change town hall hosted by CNN, a teacher named Martha Readyoff brought up population growth and said that while she recognized it's a "poisonous" topic for politicians she felt it was "reasonable" to bring up in the context of discussions on climate.

"Empowering women and educating everyone on the need to curb population growth seems a reasonable campaign to enact," Readyoff, going on to ask Sanders if he would be "courageous enough to discuss the issue."

"Well, Martha, the answer is yes," Sanders said. "The answer has everything to do with the fact that women in the United States of America, by the way, have a right to control their own bodies, and make reproductive decisions."

"The Mexico City agreement which denies American aide to those organizations around the world that allow women to have abortions or even get involved in birth control to me is totally absurd," Sanders added. "So I think, especially in poor countries around the world where women do not necessarily want to have large numbers of babies, and where they can have the opportunity through birth control to control the number of kids they have, is something I very, very strongly support."

Conservatives slammed Sanders for talking about population growth in relation to climate

Sanders was widely criticized by conservatives on social media over his comments, highlighting how thorny this issue is - particularly in the US, where abortion continues to be a hotbed political topic. 

In response to the Vermont senator's remarks, Steve Guest, the rapid response director for the GOP, tweeted: "Bernie Sanders: abort poor babies for population control."

Similarly, CNN host S.E. Cupp in a tweet said, "Let's just state for the record: talking about needing 'population control' through ABORTION for the sake of CLIMATE is talking about EUGENICS. The fact that @BernieSanders is willing to entertain this vile idea is not only disgusting, it should be disqualifying."

Read more: Joe Biden scrambles to defend his climate record at 7-hour CNN town hall

Indeed, when people hear the phrase "curb population growth" in can conjure up thoughts of eugenics, China's controversial one-child policy, and Malthusianism. 

But there's also a fair amount of research that backs up the notion improving access to birth control and voluntary family planning could help slow global warming.

For example, a 2010 study published in the Proceedings of the National Academy of the Sciences that examined the link between population growth and carbon emissions found "slowing population growth could provide 16-29% of the emissions reductions suggested to be necessary by 2050 to avoid dangerous climate change."

And a 2017 study from Lund University found having fewer children was among four high-impact ways to reduce carbon emissions in addition to living without a car, avoiding airplane travel, and eating a vegetarian diet.

"I knew this was a sensitive topic to bring up," study co-author Kimberly Nicholas said on NPR's Morning Edition in July 2017. "Certainly it's not my place as a scientist to dictate choices for other people. But I do think it is my place to do the analysis and report it fairly."

Experts have repeatedly said improving access to birth control could help curb global warming

Along these lines, experts have repeatedly pointed to improving access to contraceptives - especially in poorer countries that are more likely to bear the brunt of climate change - as a way to help slow global warming while also making it easier for communities to adjust to its impact. 

Clive Mutunga, a PHE technical advisor for the Office of Population and Reproductive Health at the US Agency for International Development, in 2016 told the Wilson Center: "Investing in family planning and reproductive health care is one of the ways that [we] can help families, individuals, and communities to better adapt to the effects of climate change."

The UN projects the global population will grow from 7.7 billion in the present day to 9.7 billion in 2050. Based on the UN's projections and data from British risk consultancy Verisk Maplecroft a recent analysis from Time found the 10 countries most vulnerable to climate change will experience population booms in the coming decades. 

Though less developed countries emit far less carbon emissions than wealthy nations like the US, they are far more at risk of being negatively affected by global warming and its byproducts. 

This helps explain why curbing population growth, albeit a sensitive issue, is becoming a central aspect of discussions on climate change.