As soon as Blythe Pepino got together with her partner Joshua two years ago, she felt “this overwhelming urge to create a family with him”, she says. “I think it was the fifth day after having met him, I said: ‘I’ve got to meet your parents.’ He was like: ‘You’re mad.’”

Then, late last year, she attended a lecture held by the direct action group Extinction Rebellion, which set out starkly the catastrophic reality of the changing climate. That galvanised Pepino, an activist and musician (she is the former singer of Vaults, now Mesadorm), to do research of her own and, eventually, to have a series of sad conversations with Joshua.

“I realised that even though I wanted to have a family at that point, I couldn’t really bring myself to do it,” she says. “I had to say to him: ‘I don’t know if I can do this, considering what we know – if there isn’t a political will to fix this, we really don’t stand much of a chance.’”

Pepino, who turns 33 today, found that other women – especially those in climate-conscious circles – were struggling with the same question, but were “too afraid to talk about it” for fear of judgment or ridicule. The US congresswoman Alexandria Ocasio-Cortez gave voice to their concerns last month, pointing to the increasingly dire scientific consensus and widespread government inaction: “It does lead young people to have a legitimate question: is it OK still to have children?”

Extinction Rebellion activists pour 200 litres of (artificial) blood outside Downing Street. Photograph: Guy Bell/Rex/Shutterstock

And so Pepino decided to publicly announce her decision – strategically making the personal political – by setting up BirthStrike, a voluntary organisation for women and men who have decided not to have children in response to the coming “climate breakdown and civilisation collapse”. In doing so, she hopes to channel the grief she feels about her decision “into something more active and regenerative and hopeful”. In just two weeks, 140 people, mostly women in the UK, have declared their “decision not to bear children due to the severity of the ecological crisis”, says Pepino. “But we have also had people get in touch to say: ‘Thank you for speaking out about something that I didn’t feel I could even talk to my family about,’” she adds. Many of these BirthStrikers are involved with Extinction Rebellion, which on Saturday threw buckets of red paint outside Downing Street to symbolise “the death of our children” from climate change.

Pepino says that BirthStrike is distinct from the antinatalist movement (which says that having children is morally wrong because sentient life is so awful), and its aim is not to discourage people from having children, or to condemn those who have them already, but to communicate the urgency of the crisis. It is a “radical acknowledgment” of how the looming existential threat is already “altering the way we imagine our future”. “We’re not trying to solve it through BirthStrike,” she says. “We’re trying to get the information out there.”

In fact, she says, population reduction has been shown to be an ineffective strategy. A 2017 study published in the Proceedings of the National Academy of Sciences of the USA explored various scenarios for global human population change by adjusting fertility and mortality rates. It found that even imposing one-child policies worldwide and “catastrophic mortality events” would not significantly reduce the global population by 2100. It proposes instead that “more immediate results for sustainability would emerge from policies and technologies that reverse rising consumption of natural resources”.

“Even with drastic, draconian, eugenic policies of population reduction – which are completely immoral,” says Pepino, “we wouldn’t save ourselves. We have to change the way we live.”

A different 2017 study did find that having one fewer child was the most effective way a person could cut their own carbon emissions – but there is damning evidence that the crisis is well past the point of being able to be mitigated by the choices of individuals.

Hannah Scott, 23, works for an environmental charity. She says that even climate activists are in denial about the gravity of the situation, with her own BirthStrike eliciting responses such as “maybe it won’t be so extreme and apocalyptic” and “life is about having children”. She believes it is already too late to claw back the damage done. “That’s why I am not having one – because I feel so desperately that it would be bringing a life into a future that does seem ever more desolate. Every time a friend tells me they’re pregnant, or planning on having children, I have to bite my tongue.”

BirthStrike, she says, “is about saying: ‘It is OK to make this choice, but it’s not OK to have to make this choice.’ We should never be in a situation where we are genuinely scared to bring life into the world.”

BirthStrike is as much a support group as it is a political statement, says spokeswoman Alice Brown, a 25-year-old charitable campaigns manager from Bristol. As a former nanny and support worker, having children of her own had been on Brown’s “to-do list for life” until one of the girls she used to care for developed allergies which, Brown says, was as a result of pollution.

Alice Brown: ‘I’m just so terrified of what my child will be facing when they are my age.’ Photograph: Sam Frost/The Guardian

Her decision was cemented with last month’s report on the “catastrophic” impact of plummeting insect numbers, and the increasingly “panicked, emergency language” of the scientific community. “We are hurtling towards disaster, and if I can bring awareness to the situation by sharing this personal choice that I’ve made, I’m willing to do it. It is sort of desperation. I don’t know if I’ll regret being so public about it one day.”

Brown is especially concerned about the potential toll her decision may have on her relationship, which she is reluctant to speak about beyond confirming that – were it not for the state of the planet – children would likely have been part of the conversation. She is keen to adopt, but worries that the option may be removed from her: she was arrested last year for civil disobedience for spraying chalk paint on the Department for Business, Energy and Industrial Strategy during a protest with Extinction Rebellion. “I hate telling people that, it sounds so childish,” she says, but she worries that further direct action campaigns could land her with a criminal record.

“I’m just so terrified of what my child will be facing when they are my age,” she says. “It’s not just about the ideology – will they be born into a world where things are fair, where things are safer – it’s the practical side of it: will they actually be in survival mode?”

There are infinite unknowns about the future, Brown agrees. She is reading the US journalist David Wallace-Wells’s apocalyptic page-turner The Uninhabitable Earth, which explores many of them – but none, she says, have persuaded her that it would be right to have a child of her own. “I understand many people may think it’s a strange response. Someone said to me the other day: ‘People still have children in war zones.’ I can only say that it is totally personal and probably no one – certainly not me – is qualified to decide what would make it worthwhile and what wouldn’t.”

But it was nonetheless a relief, she says, when Ocasio-Cortez said it was “legitimate” for millennials to consider not having children because of the state of the earth. “It makes me feel more confident and maybe more legitimate in what I’m talking about – that somebody who is in the public eye, who is taking the crisis as seriously as it should be taken, is saying the same thing.”

Yet Wallace-Wells, whose book begins “It is worse, much worse, than you think”, goes on to write about the birth of his daughter. In interviews, he has said that he wanted to have children “for reasons independent of climate … Most people do. I don’t think this is an impulse we need to disavow before we have finished the final act of this story. I think it is a reason to fight.”

If calamity proves a catalyst for change, “the greatest story ever told … may well have a happy ending”, he concludes in The Uninhabitable Future. The 10,000 young people in the UK alone who went on strike from school over climate last month and activists such as 16-year-old Greta Thunberg suggest his daughter’s generation may play a pivotal role.

Pepino, at least, takes a similarly optimistic view of BirthStrikers’ approach. It is, she says, “in a sense a very hopeful act. We’re not just making this decision, hiding it and giving it up. We’re politicising that decision – and hoping that will give us the chance to change our minds.”