We need to talk about population. If you are like most people, you don’t want to. But the truth is that at present, given the danger of environmental disaster, we don’t have the right to have more than one child, and this is something that needs to be discussed.  We’re not living sustainably with our present population of 7.3 billion, and the United Nations’ most recent estimate is that our numbers will reach 9.7 billion by 2050, and then a hard-to-imagine 11.2 billion by 2100.  And this is when the global average for women is to have about two children.  Yes, population would eventually stabilize, but if it becomes stable at an astronomically high number it will still be a disaster. This isn’t something we have a right to bring about.

Almost no one wants to interfere with people having children.  A common reaction is to say it just isn’t a problem. Critics dismiss fears about overpopulation as “neo-Malthusian.” The idea is that since Thomas Malthus was wrong in 1798 when he wrote that population would soon outgrow food production, the current gloomy estimates about population are also wrong.  However, we are obviously better at science than we were in 1798. Demographers at the U.N. aren’t a lot of mad-eyed tree-huggers.  They are scientists, whose job in life is to study fertility trends around the world. If they say 9.7 billion by 2050, they didn’t pull that figure out of a hat. Meanwhile, the International Panel on Climate Change, also a pretty reputable organization, has said that we need to cut back our emissions between 40 and 70% to keep global warming within 2° Celsius. That’s a lot.  It’s going to be hard enough to do with the number of people we have now, but almost unimaginable with 11.2 billion, or even the more modest 9.7 billion we’ll have by 2050 — within the lifetime of many who are living today.

So what should we do?  This is the question I address in One Child:  Do We Have a Right to More? (Oxford University Press, 2016.)  Some have realized that rising population is a danger. The problem is that they have found themselves without a solution, because they believe that people have a right to have as many children as they want, and so there is nothing we can do. Instead of focusing on population, they concentrate on reducing consumption.

Reducing consumption is, of course, a good idea for those of us who can do it (which isn’t everyone. Cutting back just isn’t an option for the one third of the world who live in absolute poverty, and who direly need more stuff, not less.) All the evidence, though, is that we just won’t cut back. Since the 1997 Kyoto Protocol, with its relatively modest goal of reducing the emission of greenhouse gases by 5% relative to 1990 by 2012, we have, as a planet, increased emissions significantly — in an age where we know the effects of consumption.  Will we do better when we need to cut back at least 40%?

Having more than one child when we know that consumption won’t be significantly reduced is like throwing a match on a house soaked with gasoline.  It’s not the match alone that does the damage, but if you know the gasoline is there, and then you throw the match, you have done something you don’t have a right to do.

At the same time, we have shown that we are willing to cut back on how many children we have.  The fertility rate has, after all, fallen over the past decades, simply because many people prefer to have fewer children.   What we need to do now is accelerate that process.

But again, won’t this violate rights?

No.  The truth is that there is no reason to think we have a right to have more than one child.  Sometimes we say we have a right to what we need for basic subsistence, which is why many people think that we have a right to food.  Fair enough — but this doesn’t give us a right to more than one child, because of course we can live good lives with just one child.  We do want the human race to continue, which gives us a reason to have children, and we have a basic interest in equal treatment, which would give each of us an equal right to have a child, but we certainly don’t need more than one child for that interest to be met.

Other people will say that we have more general rights — rights to live our lives as we want. We have a right to live according to our own values, to make our own life plans. Again, fair enough.  But this only goes so far.  As Oliver Wendell Holmes said, my right to swing my fist ends at the other man’s nose. The right to live as you want doesn’t mean you can live in a way that does dire harm to others.  When the world wasn’t threatened with catastrophic climate change, soil depletion, over-fishing, the extinction of species, and a growing shortage of fresh water, you could suit yourself when it came to deciding how many children to have. That’s not the world we’re in, though, and when circumstances change we need to change what we do.

Does this mean we must allow forced abortions and sterilizations? No. Those are assaults, and do violate rights. They are also completely unnecessary.  All the evidence is that we can change the fertility rate with a combination of incentives and disincentives.  We can educate. We can make contraception free and easy to get.  We can reward having fewer children with tax breaks, or disincentivize having more with tax penalties.  These are likely to be successful measures, but one of the things we need to talk about is how best to discourage people from having too many children.  To do that, though, we need to address the problem, and we need to start now.