Carbon Legacies and Responsibility; Is Having a Child Really As Bad As Taking 72 Transatlantic Flights a Year? 

Let’s face it: humans are terrible at tackling climate change. Sure, we have become great at researching it, studying it, talking about it and having it star in terrifying documentaries. We are also getting good at concluding that the accumulation of GHGs (greenhouse gases) in the atmosphere is the result of all of our individual decisions combined. We have even calculated what would need to happen on an individual level if we want to stay below the 2 °C warming target for 2100 set in Paris; by 2050, per capita emissions would have to be down to 2.1 tonnes CO2 eq. per year 1 . We also know that in 2016, we collectively emitted 49.3 gigatonnes CO2 eq. (not including land use, land-use change and forestry) 2, which comes down to about 6.6 tonnes per person. Furthermore we have realized not everyone is carbon-equal: in the EU and US, per capita emissions in 2016 were about 8.7 and 20 tonnes respectively.

Clearly, we high-carbon individuals are a long way from the average, and an especially long way from the required 2.1 tonnes per person. Most of us respond to such realizations by trying not to panic, eating a little less meat, feeling guilty about flying and waiting for too-slow top-down change to save the day. In other words, one of the reasons we’re terrible at tackling climate change is that we have so little faith in the power of our own actions. But this is not because individual actions are completely powerless; it’s because most people in developed countries don’t understand how significant their lifestyle choices are for cutting emissions fast enough.

A study published last year played into this problem by quantifying how effective different individual actions are in reducing GHG emissions. It reached a striking conclusion that spurred quite some media attention; ranked first among a dozen examined actions was “having one fewer child” – a choice that the authors claimed would save a staggering 58.6 tonnes CO2 eq. per year for a person in a developed country. Next on the list were “living car-free” with 2.4 tonnes CO2 eq. per year, “avoiding airplane travel” with 1.6 tonnes CO2 eq. per roundtrip transatlantic flight, and “eating a plant-based diet” with 0.8 tonnes CO2 eq. per year 3

Comparison of the emissions reductions from various individual actions
Comparison of the emissions reductions from various individual actions (Source: http://iopscience.iop.org/1748-9326/12/7/074024/downloadHRFigure/figure/erlaa7541f1)
So what does this mean? 

At first, I was rather unsettled after seeing these numbers; I had never consciously thought about having children as a carbon-intensive choice, let alone as the worst thing you could do to the planet. Apparently, having a single child was worse than flying over the Atlantic and back 36 times a year! Next, I started to wonder why this was not common knowledge, and why we did not advocate this as the best emission-reducing lifestyle choice (‘if one person having one fewer child has the same net effect as 73 people being vegetarians their whole lives, why bother advocating vegetarianism?’). The more I thought about this, the more questions popped up; if I have no children, can I eat all the meat I want?  But what if my kids were vegetarians and never used a car? Are the emissions of my grandchildren included? And their children? How did they even come up with that number? And most importantly: does the number even make sense? 

Before we discuss these questions, let’s hit the brakes for a second and remember we are talking about averages here. None of the numbers calculated by Wynes & Nicholas indicate how many tonnes of GHGs you and I will prevent from being emitted by performing any of the actions mentioned, because that would be entirely dependent on our current lifestyles (and in the case of having fewer children, the lifestyles of our would-be kids). This means comparisons like the 36 flights and 73 vegetarians do not actually mean anything in practice. What the numbers and comparisons do indicate, however, is the relative potential of each of these actions to prevent climate change if they were widely applied; being aware of this can help policymakers and educational institutions in determining their focus, and make consumers more conscious of the true impacts – whether positive or negative – of different choices. 

How did they even calculate the impact of having one fewer child? 

Now, let’s take a closer look at the method that was used to arrive at the 58.6 tonnes CO2 eq. yearly savings. Wynes & Nicholas chose to follow an approach taken by Murtaugh & Schlax in 2008; this paper quantified the emission of having a child by adding up the total emissions of a person’s descendants weighted by their relatedness to the person 4. According to this model, half of your child’s lifetime emissions would be attributed to you, a quarter of your grandchild’s lifetime emissions, and so on. What this adds up to is influenced by two additional factors: 1) the number of descendants in each generation, calculated from the prevailing fertility and mortality rates; and 2) the expected per capita GHG emissions in each generation. Applying this model to three different climate change scenarios (optimistic, constant and pessimistic) resulted in the graphs below. 

Average CO2 emission rates attributable to the initial parent
For the United States with medium-variant fertility rates, average CO2 emission rates attributable to the initial parent, under optimistic, constant and optimistic projections of per capita emissions. The area under each curve, extended to infinity, is the average mass of CO2 for which the ancestor is responsible. The number of children borne by the initial parent follows the 2005 fertility rate. (Source:https://www-sciencedirect-com.proxy.uba.uva.nl:2443/science/article/pii/S0959378008001003)

Using this model and more recent statistics from different countries, Wynes & Nicholas could calculate the total GHG “legacy” of an average person, and divide that by their life expectancy to arrive at the annual emission reduction achieved by having one fewer child. It sounds clever, but does it also make sense? As you may suspect, there are a few problems with this way of assigning responsibility.

Problem 1: double counting 

First, the mere fact that we all create a so-called “carbon legacy” if we choose to have children cannot mean that we are also fully responsible for these emissions in the same way that we are responsible for emissions from car rides or flights. In fact, making this assumption results in double counting, because emissions from a personal action (e.g. taking a flight) would be attributed not only to that person, but at the same time to the person’s parents (because they chose to have the child) 5.

Consequently, the model used by Wynes & Nicholas either greatly overestimates total responsibility (by attributing emissions to persons and their parents), or completely nullifies the responsibility of future generations. Both of these options seem unfair, but certainly up to ethical debate.  

Problem 2: population isn’t really the issue

Another reason why I would disagree with the classification of “having one fewer child” as first on the list of emission-reducing actions, is that it promotes a focus on decreasing the number of people to mitigate climate change. Even though overpopulation is clearly a driver, seeing it as a true cause would be a mistake. Instead, we – also in our individual choices – should prioritize fixing more fundamental issues, such as overconsumption, structural inefficiency and reliance on fossil fuels. After all, these root causes are also the reason why having a child is currently such a carbon-intensive choice.

Problem 3: would it cut emissions if people knew this? 

Finally, it is interesting to think about what would happen if people were actually informed of this impact. Wynes & Nicholas conclude that current government documents and education materials completely overlook this as a mitigating action; but would higher awareness actually result in a population decrease that was beneficial for the planet? I mean, people that choose to make such a deeply personal sacrifice to reduce their carbon impact will likely have environmentally friendly lifestyles already, and their children would probably have grown up to become people with smaller carbon footprints than the children of people that don’t care enough about climate change to have a smaller family. So, the average annual savings of 58.6 tonnes CO2 eq. per year would probably not turn out to be accurate.

Conclusion

In the end, as I indicated before, we must remember that these calculations are about averages based on averages. We can – and should – criticize their theoretical and practical accuracy, but we cannot deny that they show having a child simply is incredibly high-impact – as long as you believe that you carry responsibility for your carbon legacy. Whether that is a yes or a no, it is certainly a choice worth making consciously. 


  1. Girod B, Van Vuuren D P and Hertwich E G. (2013). Global climate targets and future consumption level: an evaluation of the required GHG intensity Environ. Res. Lett. 8 014016
  2. J.G.J. Olivier, K.M. Schure, J.A.H.W. Peters. (2017). TRENDS IN GLOBAL CO2 AND TOTAL GREENHOUSE GAS EMISSIONS. Summary of the 2017 report. PBL Netherlands Environmental Assessment Agency 
  3. Seth Wynes and Kimberly A Nicholas. (2017). The climate mitigation gap: education and government recommendations miss the most effective individual actions. IOP Publishing Ltd Environmental Research Letters, Volume 12, Number 7.
  4. Paul A. Murtaugh, Michael G. Schlax. (2009). Reproduction and the carbon legacies of individuals, Global Environmental Change, Volume 19, Issue 1, Pages 14-20, ISSN 0959-3780, https://doi.org/10.1016/j.gloenvcha.2008.10.007.
  5. Philippe van Basshuysen and Eric Brandstedt. (2018). Comment on ‘The climate mitigation gap: education and government recommendations miss the most effective individual actions’. Published by IOP Publishing Ltd. Environmental Research LettersVolume 13Number 4.

4 thoughts on “Carbon Legacies and Responsibility; Is Having a Child Really As Bad As Taking 72 Transatlantic Flights a Year? 

  1. Hey Nika, I really liked reading your article and I appreciated your critical tone. It also made me think of children in relation to climate change from a different perspective. Maybe having fewer children does not only have to be about reducing your own carbon foot print but also about how climate change is affecting children. I came across this report: https://www.unicef.org/publications/files/Unless_we_act_now_The_impact_of_climate_change_on_children.pdf
    Children suffer disproportionately when it comes to climate change and these future kids should be protected somehow for the effects of climate change. I know it is a bit different from your article but I was just wondering what you think about this issue?

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  2. @nikavos I’m not entirely surprised by the content of your blog. However, when you mentioned “mean, people that choose to make such a deeply personal sacrifice to reduce their carbon impact will likely have environmentally friendly lifestyles already, and their children would probably have grown up to become people with smaller carbon footprints than the children of people that don’t care enough about climate change to have a smaller family”, a light bulb went off in my head. Perhaps the people who are such extreme environmentalists that they avoid having children should be the ones to have them! Because let’s be honest we need more people with their mindset. Then I had another thought, what about adoption? Can we put a carbon footprint on that? Maybe instead of reproducing yourself, adopting is a more environmentally friendly option without having to give up the experience of parenthood.

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  3. Interesting to read! I remember having discussions about this several times.. I was wondering how you came to the conclusion of ‘double counting’, what you mention here: “making this assumption results in double counting, because emissions from a personal action (e.g. taking a flight) would be attributed not only to that person, but at the same time to the person’s parents”. I don’t see the double counting problem when comparing individuals. It only becomes double counting, when you want to calculate total emissions. If you want to compare people, even different generations, this method still holds. Right?

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