Q. Dear Umbra,

My boyfriend and I have been talking about (eventually) having kids. I want two, but he wants just one! Part of his reasoning is that having one kid is better for the environment. I know he’s not wrong, but how big of a deal can one extra human really be? Should the climate really be a factor in our family planning?

Offspring Fan (Not the Band)

A. Dear Offspring Fan,

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There has been a ton written about the climate-driven decision to have children. And yet millions of people are still trying to figure this question out — including you and me — because it’s extremely hard!

So, let’s do it together. I’ll tell you what I know about climate-based reproduction decisions (I have a little personal experience here), and I’ll tell you how parents who have made environmentally-centered family planning decisions feel about them.

I’d be remiss in not giving the caveat that there’s a long, ugly history of racist population control initiatives in the name of so-called environmentalism and resource conservation. I think that both you and your boyfriend should be aware of that legacy, particularly if either of you is a person of color!

With that in mind, the general wisdom of climate-conscious family planning is if you’re going to reproduce, it should be at or below the replacement fertility rate. In English, that means that you aren’t adding to population growth. Climate-based population fears basically come down to: “Humans cause climate change! We can’t have too many of them!” That’s especially true for wealthy humans in developed countries, because they have the highest environmental impacts.

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The good news for you is that the replacement fertility rate in the United States is 2.08, and the number of kids you want to have falls just below that. So you’re good. Right?

Well, that depends on how climate-conscious you want to be. In 2017, a team of Lund University researchers looked at all the personal decisions we make that influence climate change. They found that far and away the most significant thing you can do to reduce your carbon emissions is to have one fewer child. That’s a little bit of a weird guideline — is there no difference if you wanted ten kids or two?

To further explore your question, I went to one of the most carbon footprint-aware people I know. Peter Kalmus is a vehement advocate for taking responsibility for the climate consequences of one’s own lifestyle in as many ways as possible: avoiding flying, driving, eating meat, and using too much electricity. Kalmus and his wife are raising two children in Altadena, California — both of whom they had before his “climate awakening.”

“To be honest, I’m glad that they both came before I was too fully aware of this issue,” he said. “I still feel that having kids has been one of the most deeply meaningful things I’ve ever done. I’m glad with them. I didn’t have to agonize over whether or not to bring them into the world — which is kind of a copout, I know.”

At one point, Kalmus and his wife had both wanted a third child. By the time that point came around, though, Kalmus felt too guilty about the idea of reproducing over the replacement rate. But now, he says, he feels some remorse that he may have deprived his wife of a third child she’d always wanted.

I asked Kalmus’ wife, Sharon Kunde, if that was the case. Rest easy, Peter.

“This might be kind of your ‘Dating Game’ moment, but I don’t really remember environmental issues being a huge factor in our decision,” she told me. Kunde said they definitely discussed it, but the reason she was happy to stop at two was to be able to devote more attention to developing her career studying literary criticism.

All this is to say that the priorities around having kids are likely going to change. If you and your boyfriend are just starting to talk about the eventual possibility of kids, I imagine a potential pregnancy is probably some ways off.

But that doesn’t mean you shouldn’t ask your boyfriend to examine his environmental reasons for wanting to limit how many kids he has — which Kunde and Kalmus have done at length. Here’s the essence of their debate:

We feel a sense of personal limitation with what we can do when it comes to climate change because what one person can do is so limited. Why focus on winnowing down the carbon impact of your own life when your energy could be more effectively spent, say, influencing many others’ beliefs about climate change?

The problem is, the way you influence others is to lead by example. And, again, the data point to your reproductive decision being the most meaningful personal choice that you can make for climate change.

Charlotte Kaiser, who works for a conservation organization in New York City, told me that she chose to have only one child because she wanted some concrete stake in the future. Nowadays, she often feels guilty because she doesn’t know what kind of future her child is going to have — a real twist of irony, she says.

“Having a child right now, when things are not looking super great, is either a decision to bring someone into an unpleasant fate or an act of profound hope and optimism,” she told me. “You have to decide how you live with either of those.”

Why am I telling you all of these seemingly contradictory things? Because I can’t tell you, definitively, how much to consider the climate. It’s a conclusion you have to come to for yourself.

But what I think you’re really asking is how to understand why this is so important to your boyfriend. I say ask him. Where does his feeling a personal responsibility for defeating climate change come from? How does he believe he can be most powerful in staunching carbon emissions? Has he considered that closely? What are other ways you could shape your lives to reduce climate change without compromising on the kid question?

Here’s one possible answer to that last question: Raise your kids, however many you have, to think about climate change. (They probably won’t have a choice!) Talk about it with them. Make sure they have a nuanced, empowering understanding of what they can do about it at any age. In fact, Kimberly Nicholas, the co-author of that Lund University study, said this month in Elle: “It’s not so much about whether you choose to have a child, [but] about what kind of lifestyle you choose to raise that child in.”

Kalmus said that the most important thing any of us can do about climate change is talk about it. Whether to have a child is probably the most life-changing decision you’ll ever make — no pressure — and climate change is probably the biggest challenge humanity will ever have to face. That makes for a REALLY goddamn scary conversation.

Most people don’t want to talk about big scary things. But in a relationship — particularly one that you expect to be lifelong — you need to be able to talk about the absolute scariest things. That’s what makes you stronger, as a couple.

With such an uncertain future, we’re all making big scary decisions half-blind all the time. At the very least, you can take comfort in the fact that you’re trying to tackle those decisions with someone who’s being thoughtful about that uncertainty.