He's at James Madison University in southwest Virginia to talk about a "small-family ethic" — to question the assumptions of a society that sees having children as good, throws parties for expecting parents, and in which parents then pressure their kids to "give them grandchildren."
Why question such assumptions? The prospect of climate catastrophe.
For years, people have lamented how bad things might get "for our grandchildren," but Rieder tells the students that future isn't so far off anymore.
He asks how old they will be in 2036, and, if they are thinking of having kids, how old their kids will be.
"Dangerous climate change is going to be happening by then," he says. "Very, very soon."
Rieder wears a tweedy jacket and tennis shoes, and he limps because of a motorcycle accident. He's a philosopher with the Berman Institute of Bioethics at Johns Hopkins University in Baltimore, and his arguments against having children are moral.
Americans and other rich nations produce the most carbon emissions per capita, he says. Yet people in the world's poorest nations are most likely to suffer severe climate impacts, "and that seems unfair," he says.
There's also a moral duty to future generations that will live amid the climate devastation being created now.
"Here's a provocative thought: Maybe we should protect our kids by not having them," Rieder says.
His arguments sound pretty persuasive in the classroom. At home, it was a different matter.
The philosopher's personal dilemma
"I have been one of those women who actually craved to have a baby," says Sadiye Rieder, smiling as she sits next to her husband in the sunroom of their Maryland home. "To go through pregnancy and everything, that mattered to me a lot."
Sadiye also wanted a big family. She grew up among extended relatives in the Turkish part of Cyprus and says she enjoyed having people around all the time.
This was not a problem early in their marriage, as each focused on their studies. But by the time Sadiye began feeling ready for motherhood, Travis' research had delved into the morality of adoption, which led to the ethics of procreation and to its impact on the climate.
They knew they had to talk.
"It's not easy to convince a philosopher!" Sadiye says with a laugh.
Scientists warn that a catastrophic tipping point is possible in the next few decades. By midcentury, possibly before, the average global temperature is projected to rise by more than 2 degrees Celsius, the point scientists and world leaders agree would trigger cataclysmic consequences. Last year's historic Paris climate agreement falls short of preventing that, so more drastic cuts in carbon emissions are needed.
Adding to that challenge, the world is expected to add several billion people in the next few decades, each one producing more emissions.
In fact, without dramatic action, climatologists say, the world is on track to hit 4 degrees Celsius of warming by the end of the century, and worse beyond that. A World Bank report says this must be avoided, and warns of unprecedented heat waves, severe drought and serious impacts on ecosystems and "human systems."
Back in the classroom, Rieder puts this in less technical terms: 4 degrees of warming would be "largely uninhabitable for humans."
"It's gonna be post-apocalyptic movie time," he says.
The room is quiet. No one fidgets. Later, a few students say they had no idea the situation was so bad. One says he appreciated the talk but found it terrifying, and hadn't planned on being so shaken before heading off to start the weekend.
Still. Even given the apocalyptic scenarios: Can you actually expect people to forgo something as deeply personal as having children? To deny the biological imperative that's driven civilization?
Rieder and two colleagues, Colin Hickey and Jake Earl of Georgetown University, have a strategy for trying to do just that. Rieder is publishing a book on the subject later this year, and expects to take plenty of heat. But he's hardly alone in thinking the climate crisis has come to this.
"The climate crisis is a reproductive crisis"
Meghan Hoskins is among a dozen people gathered in the spare office of an environmental group in Keene, N.H., earlier this year. They sit on folding chairs in a circle, the room humming with multiple conversations.
"If I had told my boyfriend at the time, 'I'm not ready to have children because I don't know what the climate's gonna be like in 50 years,' he wouldn't have understood. There's no way," says Hoskins, a 23-year-old whose red hair is twisted in a long braid.
This is one of 16 meetings over the past year and a half organized by Conceivable Future, a nonprofit founded on the notion that "the climate crisis is a reproductive crisis."
Hoskins says she's always wanted "little redheaded babies" — as do her parents, the sooner the better.
But she's a grad student in environmental studies, and the more she learns, the more she questions what kind of life those babies would have.
In a country where even the idea of climate change can be polarizing and political, Hoskins has never shared that fear until now.
Meghan Kallman is a co-founder of Conceivable Future. "I can't count the number of times people have said, 'Oh, my God, it's so nice to know I'm not the only person that worries about this,' " she says.
In November 2014, Kallman and Josephine Ferorelli created Conceivable Future to make these personal struggles public. The group's ultimate goal is ending U.S. fossil fuel subsidies, though its immediate role seems one of commiseration.
Conceivable Future targets climate activists immersed in scary data. There's already a term for how some feel: climate trauma.
But Kallman and Ferorelli say the focus on numbers fails to capture the emotion that drives many to work on the issue in the first place. For activists of childbearing age, Ferorelli says, climate change isn't just an intellectual problem but "a heart problem."
Ferorelli, 33, and Kallman, 32, are both in committed relationships, and in the throes of this problem. Ferorelli recently helped her widowed mother pack up her house, saving cherished items with the unspoken assumption that they are for a next generation.
And yet, when she imagines raising a child, Ferorelli says she can't help but envision the nightmare scenarios that have dogged her since she first heard the term "global warming" in elementary school.
"Knowing that I gave that future to somebody is something that just doesn't sit very well," she says.
At the New Hampshire meeting, 67-year-old Nancy Nolan tells two younger women that people didn't know about climate change in the 1980s when she had her kids. Once her children were grown, "I said to them, 'I hope you never have children,' which is an awful thing to say," Nolan says, her voice wavering. "It can bring me to tears easily."
She adds that of course people are driven to procreate, and you can't really tell them not to.
One woman looks a little stunned. She's not a climate activist — just tagged along with a friend — and says she had no idea that deciding not to have kids because of the climate was even a thing.
These aren't the first would-be parents to ask whether it's fair to bring a child into the world. U.S. birth rates plummeted during the Great Depression. Many also must have thought twice amid warnings of overpopulation in the 1960s and '70s, and under the threat of nuclear holocaust.
Carbon Emissions, A Comparison
Below are a few examples of how much carbon dioxide (in metric tons) is saved over a lifetime (80 years) by a typical American for certain actions, including not having one child.
Increase car's fuel economy from 20 to 30 mpg: 148
Reduce miles driven from 231 to 155 per week: 147
Replace single-glazed windows with energy-efficient windows: 121
Replace ten 75-watt incandescent bulbs with 25-watt energy-efficient lights: 36
Replace old refrigerator with energy-efficient model: 19
Recycle newspapers, magazines, glass, plastic, aluminum and steel cans: 17
Reduce number of children by one (with emissions fixed at 2005 per-capita values): 9,441
What's your carbon footprint? Use the EPA's calculator to get an estimate.
Kallman says she's heard from women who remember that; their reaction surprised her.
"Things like, 'Oh, I thought we were gonna blow ourselves up in nuclear war, but it didn't happen. And therefore, just be quiet and have some babies, and, see, everything will be all right,' " she says.
The comments may be well-intentioned, but as Kallman and Ferorelli see it, the threat from climate change is worse. It's not a possibility. It's happening.
Not everyone at the New Hampshire meeting is as pessimistic about the future. Becky Whitley still plans to have a second child. She's with the advocacy group Moms Clean Air Force and says becoming a parent is precisely what motivated her to care about the climate.
"I think I really do come from a place of hope because I am a mother," she says.
Kallman and Ferorelli say they don't want to tell anyone what to do. In fact, neither is ready to rule out children herself.
"I'm not ready to get rid of the fantasy," says Ferorelli. "In certain versions of the future, I would love to have a kid."
An easier way?
Back at James Madison University, Travis Rieder explains a PowerPoint graph that seems to offer hope. Bringing down global fertility by just half a child per woman "could be the thing that saves us," he says.
He cites a study from 2010 that looked at the impact of demographic change on global carbon emissions. It found that slowing population growth could eliminate one-fifth to one-quarter of all the carbon emissions that need to be cut by midcentury to avoid that potentially catastrophic tipping point.
Rieder's audience seems to want an easier way. A student asks about the carbon savings from not eating meat.
Excellent idea, Rieder says. But no amount of conservation gives you a pass. Oregon State University researchers have calculated the savings from all kinds of conservation measures: driving a hybrid, driving less, recycling, using energy-efficient appliances, windows and light bulbs.
For an American, the total metric tons of carbon dioxide saved by all of those measures over an entire lifetime of 80 years: 488. By contrast, the metric tons saved when a person chooses to have one fewer child: 9,441.
Another student asks: "What happens if that kid you decided not to have would have been the person who grew up and essentially cured this?"
Again, great question, says Rieder, but the answer is still no. First, the chances are slim. More to the point, he says, valuing children as a means to an end — be it to cure climate change or, say, provide soldiers for the state — is ethically problematic.
With all that's at stake, he says, we need to shift our cultural attitudes. "It's not the childless who must justify their lifestyle. It's the rest of us."
And that includes Rieder.
"One and done"
At home, Travis Rieder's face lights up when his 2-year-old daughter, Sinem, sings a favorite song. She stands at her mother's knee, bouncing up and down on her toes, giggling as her parents clap.
After many conversations, he and Sadiye ended up convincing each other. Travis decided you can't deny someone the hard-wired human fulfillment of creating a child.
But Sadiye agreed that the moral bar for a second child is much higher. The couple is "one and done." Any more children will come through adoption.
Travis also argues that someone who doesn't feel that deep longing to procreate is morally compelled to think twice before having any children at all.
When he writes online, Rieder often gets nasty comments, and inevitably people will say he must not have children. He believes it's important that he understand viscerally what he's asking of people. His daughter, he says, is "the most amazing thing we've ever done with our lives."
So how do you persuade millions or billions of people around the world to sacrifice that? To avert climate disaster, the fertility rate would have to fall much faster than it has been. It would require more than educating women and expanding access to contraception, as aid agencies have been doing for decades.
Carrots for the poor, sticks for the rich
Rieder and his Georgetown collaborators have a proposal, and the first thing they stress is that it's not like China's abusive one-child policy. It aims to persuade people to choose fewer children with a strategy that boils down to carrots for the poor, sticks for the rich.
Ethically, Rieder says poor nations get some slack because they're still developing, and because their per capita emissions are a sliver of the developed world's. Plus, it just doesn't look good for rich, Western nations to tell people in poor ones not to have kids. He suggests things like paying poor women to refill their birth control and — something that's had proven success — widespread media campaigns.
In the 1970s and '80s, a wave of educational soap operas in Latin America, Asia and Africa wove family planning into their plot lines. Some countries did this when they faced economic crisis. The shows are credited with actually changing people's opinions about family size.
For the sticks part of the plan, Rieder proposes that richer nations do away with tax breaks for having children and actually penalize new parents. He says the penalty should be progressive, based on income, and could increase with each additional child.
Think of it like a carbon tax, on kids. He knows that sounds crazy.
"But children, in a kind of cold way of looking at it, are an externality," he says. "We as parents, we as family members, we get the good. And the world, the community, pays the cost."
Of course, there are ethical concerns. Rebecca Kukla of Georgetown University worries about stigma, especially against poor and minority women. If cultural norms do change, she says, there could be a backlash against families with more children than is deemed socially appropriate.
Kukla appreciates that Rieder's penalty on procreation would be progressive. But since it could not be so high as to be coercive, she says it would inevitably be unfair.
"What that will actually translate into is it becoming much easier for wealthy people to have children than for other people to have children," Kukla says.
An even bigger hurdle is the sheer unlikelihood of it all. Rieder has no illusions. In fact, he says, some countries that have successfully reduced fertility rates have since reversed course, afraid that falling population will hurt their economies. (He has an answer — just as controversial — to that, too. He would have nations open up immigration to allow in the expected tens of millions of climate refugees.) Rieder's real hope is to change people's way of thinking about childbearing.
But if his idea seems like a last-ditch Hail Mary play, he wouldn't disagree.
"The situation is bleak, it's just dark," he says. "Population engineering, maybe it's an extreme move. But it gives us a chance."
Still, Rieder wonders: Is it really so crazy? Scientists have proposed incredibly risky schemes to geoengineer the clouds and oceans. They're researching ways to suck carbon out of the air on a mass scale. Some have even called for overhauling the global system of free-market capitalism.
Compared to all that, Rieder says, bringing down the fertility rate seems downright easy.
"We know exactly how to make fewer babies," he says. And it's something people can start doing today.