Climate Action — Children


I’m nervous writing about this topic. Research suggests that when people feel climate change science is critical of their choices, they reach by attacking the science or attacking scientists’ own lifestyles.

Please do not Galileo me.
Source: Guardian

Unless you will ever contemplate lighting a forest fire, the decision to reproduce is probably the biggest carbon choice you will ever make.

How Bad are Bananas, Mike Berners-Lee (2013)

To emphasise: I know that when people tell you that driving/flying/eating meat/having a child causes a lot of emissions, they’re almost always trying to get you to stop. I’m not. I think the job of scientists is to give people their findings as clearly and accurately as possible, without exaggerations and without omissions, and stop there. Science isn’t a weapon for manipulating people.


58.6 tons per child per year

The figure 58.6 tons of emissions per child per year is widely quoted in mainstream media articles. It and the other numbers in the Guardian infographic above were taken from a paper called (The) Climate Mitigation Gap. That paper draws on an earlier paper, Reproduction and the Carbon Legacies of Individuals, which I’ll call Carbon Legacies. The authors of Climate Mitigation Gap also produced a follow-up FAQ.

  • Emissions are added up until an end date, which isn’t specified in Carbon Legacies. The choice of date makes a big difference to the final figure.
  • Carbon Legacies considers several emissions reduction trajectories, but they are pretty arbitrary, not grounded in the data.
  • Dividing the Carbon Legacies figures by life expectancy is not really meaningful…
  • and nor is averaging over three randomly chosen developed countries.

How Bad are Bananas

Berners-Lee provides his own calculation for the emissions from having a child; in the 2011 edition of How Bad are Bananas, he cites 688 tons for an average US child and 373 tons for the UK, based on the assumption that emissions will drop by 3.9% a year.

Other Research

There haven’t been other quantitative estimates of the warming resulting from a child, at least in the 350 or so papers that cite Climate Mitigation Gap. There is plenty of related work, though. Everything I have found concurs that having that having children has a very large impact on warming.

To be fair, not all journalists are like this. Just most of them.

Science versus Journalism

If you read Climate Mitigation Gap and see what they’re actually claiming to do, all they say is that they consider individual choices and

Emissions and Sins

Hidden in many of these straw men is the idea that emissions are sins. If there’s global warming happening, someone, somewhere has done something bad and we need to point a finger at them and jump up and down. This idea leads naturally to the viewpoints discussed above: if your children’s emissions are their sins, they can’t be your sins.

Calculating the Impact

I’m not comfortable using any of the numbers above, because they all depend on very arbitrary assumptions about how fast emissions will decrease and about how many generations to consider. So we’ll redo the Climate Mitigation Gap calculation with those issues fixed.

Emissions Decrease

The US, the UK, and other developed countries are reducing emissions per person, if more slowly than most people think. I ended up writing a whole other (long) article on this, which has all the sources. Here are some highlights for per-capita emissions:

  • UK consumption emissions dropped 1.2% a year.
  • UK emissions are projected to drop 1.7% a year to 2035.
  • US consumption emissions dropped 0.54% a year.
  • US emissions are projected to drop 0.71% a year to 2050.

Grandchildren and great-grandchildren

Because we’re looking at the temperature at a particular date (2100), there’s an objectively correct way to decide how many generations to track. We want to consider all the emissions before 2100, and only those. In practice, if you decide to have a child now,* you’ll likely have grandchildren around 2051 and great-grandchildren around 2081.

  • your child from 2021 to 2099
  • your grandchildren from 2051 to 2099
  • your great-grandchildren from 2080 to 2099.
From here and here.

The Final Calculation

We’re now ready to do the final calculation. As a reminder, we’re computing the impact of one child; we assume 0.9 grandchildren in 2051 and 0.81 great-grandchildren in 2081. Rather than using a fixed annual emissions reduction, I’ll show you the effect of a range of parameters. For comparison, I’ll also add your ‘direct’ emissions, assuming you’ll live another 50 years.


I’ve been told that a large family with a ‘green’ lifestyle might result in the same emissions as an small family with an average lifestyle. That’s prima facie plausible, but I just can’t square it with the research I’ve read. There are two problems.

On the Little Planet

If you’ve read the main article, you’ll know we’re turning emissions figures into something more comprehensible by illustrating their effect on a Little Planet which is 7.8 billion times smaller than Earth.

  • For an average US person, each child increases their Little Planet’s 2100 temperature by 2.2 °C.
  • For an average UK person, each child increases their Little Planet’s 2100 temperature by 1.4°C.
Source: Guardian



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