"Have one fewer child"

I’ve been looking for suggestions of individual actions one can take to reduce CO2 emissions. In particular, ones which actually make a big difference (unlike, e.g., switching to LED lightbulbs). Everywhere I look, all I see is "have one fewer child" dwarfing all other actions by effectiveness. It's all anyone talks about.

Graph showing comparative impacts of different climate actions. "Have one fewer child" so overshadows others that the y-axis has been clipped to accommodate it.
Wynes & Nicholas (2017, Environmental Research)

The Web is full of figures like this one. It shows the one-fewer-child recommendation being equivalent to about 60 t/y, where the next-best options like “sell your cars”, “stop flying” or "be vegan" are mostly in the 1–2 t/y range. So high, they had to clip and compress the range on the graph so you could even see anything else. That looks pretty stark. That figure is so high, it seems as if nobody could ever hope live sustainably if they had even one child. They might as well be taking a long-haul flight every 10 days for the rest of their life! Now, we definitely shouldn't discount conclusions just because they are surprising or uncomfortable, but we should scrutinise them. That feeling of "…really?" is the first hint something might not be right.

This specific recommendation seems to come from a 2017 paper by Wynes and Nicholas (whence the above image), which compares various individual actions by their effectiveness. They report results which gave rise to the above figure, and of course with such a shocking headline result, it got a lot of initial media coverage and attention-economy churn.

There are a lot of problems with this paper, such as the fact that potentially highly impactful (?) actions like “switch banks” and “insulate your house” weren’t included in the comparison, or that the politically and ethically charged headline recommendation was not treated with appropriate political and ethical consideration. Many criticisms have been laid out in various published replies (e.g. van Basshuysen & Brandstedt, 2018; Laycock Pedersen & Lam, 2018), but since there's one I came up with independently (though it's in the other replies too), I thought I’d write about it here.

As far as I can tell, the way the value of emissions associated with having a child was calculated was just made-up, and it seems to me to be kind of nonsensical. To be fair to the authors, they didn't come up with the method themselves, and the purpose of their paper is to collate and compare recommendations proposed by others; but given the extraordinary conclusion, ethical implications and questionable methodology, they should perhaps have adopted a more critical approach.

The authors base their calculation on a method proposed by Murtaugh and Schlax (2009). The method works like this (I'm glossing over the details): find the average emissions per capita of the world (4.31 t/y as of 2005) and the average number of children per woman (as they describe it; 1.85–2.05). Then the personal responsibility for emissions incurred by having a child are equal to:

  • ½ of the child's lifetime emissions (the other half goes to the other parent),
  • plus ¼ of their offspring’s lifetime emissions (the other ¾ go to the other 3 grandparents),
  • plus ⅛ of their offspring’s lifetime emissions,
  • and so on, summed to infinity.
  • Then divide that total by the individual’s expected lifespan (80) to get the per-year number.

Murtaugh and Schlax do some more detailed analysis breaking down predicted trends in these values, and distributions over different regions, running simulations for different scenarios. Wynes and Nicholas just take the one figure, though. But in short, the framework is: everyone is responsible for the lifetime emissions of their extended offspring in proportion to how much genetic material they share. The justification for this is that the child’s emissions, and that of all their infinite descendants, would never occur if the child was not born, and thus it is the having of the child which confers proportional responsibility to the parents.

But there are (at least) a couple of problems with this approach:

  1. Emissions are multiply counted as generations progress.
  2. It has a bonkers conception of how intergenerational responsibility works.

To explain point 1: my kid is presumably fully responsible for their own emissions, as I am for mine. But I and their other parent are also each counted as ½ responsible for those same emissions, so those emissions have been fully counted twice in terms of responsibility: once by the child, and once by the combined parents. A grandkid’s emissions are fully accounted for three times: entirely covered by the grandkid themself, also entirely covered by their parents (bearing ½ each), and also entirely covered by their four grandparents (bearing ¼ each). And so on: by the n-th generation you’re double-counting responsibility for each given emission n times. It's true that partners in crime are each fully responsible for their joint actions, but this cascading down all future generations is the second hint to me that something isn’t quite right.

To explain point 2: it assumes that someone's parents bear total responsibility for their entire lifetime actions. Consider an analogy: I am responsible for murders I commit. I am arguably responsible for murders my child commits before the age of 18. But am I responsible for ½ the murders they commit as an adult? Are my parents? Is that how anybody understands responsibility?

In fact, following this logic, if the child and the parents are both fully responsible for the lifetime emissions of the child, then why divide that responsibility between the parents? If both of the parents and the child are necessary participants in the child's eventual emissions, why doesn't each parent bear full responsibility, just as the child does? The answer to this is obviously that this would make having a child associated with responsibility for infinite emissions, more than will ever actually be emitted (oops), but the method would seem more consistent with the responsibility framework Murtaugh and Schlax propose. Dividing responsibility via percentage of shared genetic material seems to me to have been an arbitrarily included step to hide the absurd implications of the method.

I propose an alternative way to do responsibility arithmetic for future emissions: each person is responsible for their own actions, and responsible for the actions of their kids, until this kids are old enough to be responsible for their own actions. Let’s conservatively say that’s the age of majority. Here, you aren't fully responsible for your offspring's actions taken as an adult, you don’t double-count your kids’ actions, and so (unless your kid becomes a parent before they are 18), you don’t get the infinite regress of diminishing fractional multi-counted responsibility for all future time. To me, this seems more rational and more in line with what people actually mean by "responsibility" (see above murder analogy).

So let's back-of-the-envelope the cost under this new measure. The additional emissions you are responsible for when having a child are:

(years of their life where you are responsible for their actions) × (their expected yearly emissions) ÷ (expected years of your remaining life).

That final division is just to convert it into a per-year figure, to make it comparable with other lifestyle changes, just like in Wynes and Nicholas's method. This new formula is more harsh than the original: it doesn't divide responsibility between parents, and it calculates per-yer equivalents using remaining life not total life. That works out (assuming kids at 30) at:

18 × 4.31 ÷ 50 = 1.55 t/y.

Assuming you and your kid are at the 2005 global average (and please, try not to be!), that’s the equivalent of 1.55 t/y for the rest of your life, equivalent to taking a long flight every year. Don’t get me wrong, that’s not nothing. It’s still clearly a decision which shouldn't be taken lightly (on climate grounds, also obviously on its own grounds). When my partner and I decided to have children, we were aware that we'd need to offset that in other ways. But it leaves room for your kid to grow, to have their own agency, for them to be better than you and make you better than you were, and for them have a net-positive impact on the world and the climate. And it’s hardly the "worse than anything else you could do" headline figure which has spread around the Net.

I hope this is not motivated reasoning in justification of my own decision to have children. I think the original method is flawed and doesn’t fit with how we conceptualise parental responsibility. Living sustainably is the issue, and it will be until we either collectively manage it or we don't. The transition will already be painful (growth capitalism has got to go), so it is deeply unhelpful to throw up attention-grabbing, philosophically cranky suggestions, especially in a scientific paper. I suspect telling people with kids that they've failed before they've started, or telling someone the one thing that gives their life meaning is actually an indefensible indulgence, is as unhelpful and demotivating as telling people they do their bit by not pre-rinsing dishes. And telling people that with authority when it's a hypothetical reach at best?

This of course totally aside from the other ethical issues with that being the top recommendation in a scientific paper, as Twitter user Ben Bowman pointed out:

In the end, this leaves me still looking for individual actions to take. I've done all the others on that list, except we have an electric car (currently powered by about 50% wind/solar, somewhat mitigating its impact). If I run out of meaningful individual actions to take, that probably leaves direct action as the next available step.

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