Shortly after Blythe Pepino decided that she wanted to have children, she realized that the idea of bringing kids into a world affected by climate change was making her uncomfortable. “It had only been a couple of years that I’d felt the desire to have kids because I’d met my partner, whom I’m deeply in love with,” she says. “I got to that point in my life where a lot of my friends were having kids and it suddenly seemed like a beautiful idea to me. And that happened to coexist with my becoming much more aware of the climate challenge.”

Pepino, a 29-year-old musician, started bringing up the idea with other women in environmental advocacy groups. “I said, ‘You’re around my age: What are you thinking about kids?'” she says. “I was able to ask that question to a few people, and I was really surprised that there were a lot of people who were saying, ‘I haven’t talked about this to anyone, but I’m really questioning it.'”

She started a Facebook group called #Birthstrike to make the idea public; within a few days, 90 women had joined. While some may be partly motivated by the fact that the choice limits carbon emissions–one recent study found that not having children is one of the most effective ways to limit your personal carbon footprint–the underlying motivation was wanting to avoid bringing a child into a world where they may suffer. “Our main focus is the fact that we’re too afraid really to bring a kid into that future,” Pepino says. After Alexandra Ocasio-Cortez recently suggested that some young Americans feel the same way, a survey found that 38% of 18- to 29-year-old Americans believe that a couple should consider the risks of climate change before deciding to have kids. “I can’t have a child unless I am seriously, seriously convinced that we are on a different path,” one member of Birthstrike, 22-year-old Alice Brown, says in a video about the group.

The group doesn’t suggest that others need to make the same choice, and members sign a declaration saying that they “stand in compassionate solidarity” with parents and don’t endorse population control as a solution for climate change. Just as some women in the middle of the 20th century might have decided to have children despite understanding the threat of nuclear war, Pepino says she understands why some people who fully understand the risks of climate change may still decide to have children. (The author of The Unhabitable Earth, a recent book that outlines catastrophic climate risks in painful detail, is among those who recently decided to have children.)

Pepino is not optimistic that the world will make the necessary changes to address climate change in time, “but that doesn’t stop me from trying to make it happen,” she says. “I’m amazed at people like Greta Thunberg–she’s so young and so she’s fighting so hard. And humans have made incredible turnabouts in the past.” Choosing not to have children also gives her more freedom to work as an activist. Still, she says, the scale of the challenge now is unprecedented, and the world hasn’t ever made this type of radical change in the past.

Being public with such an emotional decision is one way to underline the urgency of the need for that change. “This is my way of saying, come on, guys, I’m almost out of hope,” she says. “So let’s put everything into this, because I feel it so severely that I’m not having children, and neither are these other people.”