Add this to the list of decisions affected by climate change: Should I have children?

It is not an easy time for people to feel hopeful, with the effects of global warming no longer theoretical, projections becoming more dire and governmental action lagging. And while few, if any, studies have examined how large a role climate change plays in people’s childbearing decisions, it loomed large in interviews with more than a dozen people ages 18 to 43.

A 32-year-old who always thought she would have children can no longer justify it to herself. A Mormon has bucked the expectations of her religion by resolving to adopt rather than give birth. An Ohio woman had her first child after an unplanned pregnancy — and then had a second because she did not want her daughter to face an environmental collapse alone.

Among them, there is a sense of being saddled with painful ethical questions that previous generations did not have to confront. Some worry about the quality of life children born today will have as shorelines flood, wildfires rage and extreme weather becomes more common. Others are acutely aware that having a child is one of the costliest actions they can take environmentally.

The birthrate in the United States, which has been falling for a decade, reached a new low in 2016. Economic insecurity has been a major factor, but even as the economy recovers, the decline in births continues.

And the discussions about the role of climate change are only intensifying.

“When we first started this project, I didn’t know anybody who had had any conversations about this,” said Meghan Kallman, a co-founder of Conceivable Future, an organization that highlights how climate change is limiting reproductive choices.

That has changed, she said — either because more people are having doubts, or because it has become less taboo to talk about them.

Facing an uncertain future

If it weren’t for climate change, Allison Guy said, she would go off birth control tomorrow.

But scientists’ projections, if rapid action isn’t taken, are not “congruent with a stable society,” said Ms. Guy, 32, who works at a marine conservation nonprofit in Washington. “I don’t want to give birth to a kid wondering if it’s going to live in some kind of ‘Mad Max’ dystopia.”

Parents like Amanda PerryMiller, a Christian youth leader and mother of two in Independence, Ohio, share her fears.

“Animals are disappearing. The oceans are full of plastic. The human population is so numerous, the planet may not be able to support it indefinitely,” said Ms. PerryMiller, 29. “This doesn’t paint a very pretty picture for people bringing home a brand-new baby from the hospital.”

The people thinking about these issues fit no single profile. They are women and men, liberal and conservative. They come from many regions and religions.

Cate Mumford, 28, is a Mormon, and Mormons believe God has commanded them to “multiply and replenish the earth.” But even in her teens, she said, she could not get another point of doctrine out of her head: “We are stewards of the earth.”

Ms. Mumford, a graduate student in a joint-degree program at Johns Hopkins and Brigham Young Universities, plans to adopt a child with her husband. Some members of her church have responded aggressively, accusing her of going against God’s plan. But she said she felt vindicated by the worsening projections.

A few years ago, she traveled to China, where air pollution is a national crisis. And all she could think was, “I’m so glad I’m not going to bring a brand-new baby into this world to suffer like these kids suffer.”

‘Some pretty strong cognitive dissonance’

For many, the drive to reproduce is not easily put aside.

“If a family is what you want, you’re not just going to be able to make that disappear entirely,” said Jody Mullen, 36, a mother of two in Gillette, N.J. “You’re not just going to be able to say, ‘It’s not really good for the environment for humans to keep reproducing, so I’ll just scratch that idea.’”

And so compromises emerge. Some parents resolve to raise conscientious citizens who can help tackle climate change. Some who want multiple children decide to have only one.

For Sara Jackson Shumate, 37, who has a young daughter, having a second child would mean moving to a house farther from her job as a lecturer at the Metropolitan State University of Denver. She is not sure she can justify the environmental impact of a larger home and a longer commute.

But for Ms. PerryMiller, the Ohio youth leader, the thinking went the opposite way: Once she had her first child, climate change made a second feel more urgent.

“Someday, my husband and I will be gone,” she said. “If my daughter has to face the end of the world as we know it, I want her to have her brother there.”

Laura Cornish, 32, a mother of two near Vancouver, said she felt “some pretty strong cognitive dissonance around knowing that the science is really bad but still thinking that their future will be O.K.”

“I don’t read the science updates anymore because they’re too awful,” she said. “I just don’t engage with that, because it’s hard to reconcile with my choices.”

‘The thing that’s broken is bigger than us’

People who choose not to have children are used to being called “selfish.” But many of them see their decision as a sacrifice.

Parenthood is “something that I want,” said Elizabeth Bogard, 18, a freshman at Northern Illinois University. “But it’s hard for me to justify my wants over what matters and what’s important for everyone.”

This attitude seems particularly common among people who have seen the effects of climate change firsthand.

Hemanth Kolla is from Hyderabad, in India, where drought and scorching heat waves have been deadly. He lives in California, where the threat of wildfires is increasing and a six-year drought only recently ended. Mr. Kolla, 36, said it felt wrong to have a child when he did not believe the world would be better for him or her.

And Maram Kaff, who lives in Cairo, said she had been deeply affected by reports that parts of the Middle East may be too hot for human habitation by 2100.

“I’ve seen how Syrian refugees, who are running from a devastating war, are being treated,” Ms. Kaff, 33, said in an email. “Imagine how my children will be treated if they have to flee their country due to extreme weather, drought, lack of resources, flooding.”

“I know that humans are hard-wired to procreate,” she said, “but my instinct now is to shield my children from the horrors of the future by not bringing them to the world.”

Ms. Kallman and Josephine Ferorelli, the founders of Conceivable Future, said that the predominant emotion at their gatherings was grief — and that the very existence of these conversations should spur political action.

“These stories tell you that the thing that’s broken is bigger than us,” Ms. Ferorelli said. “The fact that people are seriously considering not having children because of climate change is all the reason you need to make the demands.”

Most of the people interviewed, parents and non-parents alike, lamented having to factor climate change into their decisions at all.

“What kind of nightmare question is that?” asked Ms. Guy, the Washington nonprofit worker. “That we have to consider that?”