Erica Gies is an independent journalist who writes about the core requirements for life — water and energy — for The New York Times, the Guardian, The Economist, and National Geographic, among other outlets.

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“Do you have children?”

It’s a question I’ve gotten repeatedly in my travels, as cultures everywhere celebrate children and women’s ability to produce them. I don’t, nor do I plan to for reasons both personal and environmental. But not wanting to spark an awkward exchange, I’d usually demur with, “Not yet.”

I found it difficult to be up front about my choice because citing overpopulation and its environmental implications as a reason not to procreate has been a conversational third rail. After all, most cultures have traditions founded on some version of the Bible’s “go forth and multiply.”

But such exhortations came long before the world population hockeysticked in the 20th century from 1.6 billion in 1900 to 6.1 billion in 2000, before climate change began melting the glaciers that supply drinking water for billions of people. Today, sea levels are rising, threatening those who live in coastal cities and turning aquifers saline. Water insecurity caused in part by population pressure factors into armed conflicts, such as the war decimating Syria. We are pushing other species toward extinction at a rate 1,000 times higher than the pre-human rate, which is sure to affect us in ways we don’t yet understand.

Technology optimists are convinced that human ingenuity will save us, as the Green Revolution doubled crop yields. But while people are working to make human activities more sustainable, increasing population blunts their impact. Consider California’s efficiency requirements for appliances, which reduced their energy use to just 25 percent of those 40 years ago. Unfortunately California’s population nearly doubled during that time, so power consumption has barely budged.

Others argue that consumption is a bigger problem than population. After all, the carbon impact of a child born in the United States (including its descendants) is more than 160 times the impact of a child born in Bangladesh. However, population and consumption are linked. History shows that rapid population growth is usually followed by a period of rising per-capita consumption such as we’re seeing in China now. Plus, globalization is bringing urban sprawl, car ownership, a disposable mentality, and a meat-heavy diet to billions more currently underachieving consumers. And ultimately, actions to green one’s lifestyle are less effective than having fewer children. An American woman driving a more fuel-efficient car, improving the energy efficiency of her house, recycling, and making similar lifestyle changes would save 486 tons of CO2 emissions during her lifetime, while choosing to have one less child would save 9,441 tons.

If we don’t curtail our numbers proactively, nature will do it for us, harshly and suddenly, via disease, famine, drought, mega-storms, or wars. I’m not advocating for a worldwide “one child” policy or authoritarian sterilizations. Rather, the key to reducing population is education for girls and access to birth control. That has been pretty effective in developed countries and developing countries, such as Thailand and Vietnam, are starting to show declining fertility rates too. But we still need a shift in social attitudes.

People act as if my choice is dangerously subversive and threatening. Family, friends and strangers have told me that I’m selfish. That I just don’t know what I’m missing. That I’ll regret it when I’m old and have no one to take care of me. That I’m somehow defective because I love my cat rather than a child. That I’m hypocritical because my cat also has an ecological footprint. But the average American contributes 17 metric tons carbon a year into the atmosphere. And while I don’t actually know my cat’s carbon pawprint, he’ll have a shorter lifespan than a child, definitely won’t be procreating, and doesn’t make a habit of driving, flying, heating the house, or buying resource-intensive electronics.

I first wrote about my decision in 2011, when I noted that the world population had doubled in my lifetime, to 7 billion. While some feedback was hostile, including people who told me I should kill myself (so if you were considering that, no need!), other people have thanked me for articulating their views. Many are non-Western, such as the 29-year-old man who said the struggle to survive in overpopulated India led him to decide against having kids, a view that is anathema to his family. “Unlike in the West where not having a child is seen as an act of selfishness,” he wrote, “Indians think of it as a complete personal failure.”

In his classic treatise “On Liberty,” John Stuart Mill argued that your right to do what you want ends at the point at which it infringes on someone else’s rights. I’d argue that, given our extreme population, having more that two kids, the replacement level for a couple, is impinging upon other people’s liberty by using their share of resources. Still, government incentives are skewed, offering tax credits for reproduction, thereby penalizing people without kids. That needs to change.

People without biological kids can still give to the next generation. Adoption provides desperately needed love and stability to a child who’s already here. I was adopted, as were two of my nephews. And in recent years, I have become a stepmother to two smart, warm, fun kids. It’s a role both enlightening and challenging, pushing me to grow as I strive to be a positive influence in their lives.

When I consider their future and the healthy planet they need to thrive, I hope that we will continue to move toward greater social acceptance of being childfree, better government policies, and more widespread education for women as a soft path to reducing our numbers. For optimal quality of life, we need fewer of us.