Our lifestyle choices determine our individual carbon footprints, including the decision whether or not to have children. In these posts, Philippe van Basshuysen and Eric Brandstedt debate whether parents should be held responsible for the emissions of future generations.

Let me say this right away: as long as we live in a society that critically relies on fossil fuels, population increase will lead to higher carbon emissions and it follows that we can reduce the expected carbon levels in the atmosphere by bringing fewer children into the world.

In a widely discussed study, Seth Wynes and Kimberly Nicholas (2017) quantify the expected emissions that are caused by different lifestyle choices of persons in developed countries. They show that, under current conditions, if a person decides to have one less child her emissions amount to almost 60 tons less CO2e1 annually. Which makes it by far the most effective lifestyle choice with regards to anthropogenic climate change, assuming per capita emissions will not rapidly decrease and approach zero (more on this below). Compare it to the second most effective choice, namely to live car-free, which saves little more than 2 tons CO2e.

Now, a different question is what normative recommendations to draw from these findings. The question I shall concentrate on here is who bears responsibility for the emissions of future people. Scientists and philosophers are debating this question heatedly (see Basshuysen & Brandstedt (2018) and Wynes & Nicholas (2018)), and it has figured prominently in the media. Let me sketch the problem, my solution to it, and what lessons I believe should be drawn from this.


The problem of quantifying responsibilities for future emissions

When considering the emission consequences of the choice to have a child, responsibility and causal contribution seem to fall apart. Unlike for example the choice to drive a car, having children does not directly release carbon dioxide. But children grow up and, just like you and me, emit through their consumption behaviour – their mobility, housing, eating habits and so on. Their parents causally contributed to those emissions by creating the persons who produce them. Who is responsible for those emissions? The children, their parents, both?

All three options seem problematic. If parents were alone responsible for their children’s emissions then we wouldn’t treat children as persons who are responsible for their own emissions, which would be wrong. On the other hand, suppose the direct polluter is alone responsible, that is, parents are not responsible for their children’s emissions. Then it would follow that having children would play no role in the calculation of individual emissions. Which would again be wrong: some of us will be among the first generation to testify, around 2100, the largest human population that the earth will ever see (see Figure 1). Even if per capita emissions will decrease substantially until then, the number of humans could outweigh those reductions, and I am not optimistic about the prospects of proceeding to a zero-carbon society soon.2 If you causally contribute to more emitting people then, arguably, you carry some responsibility for those emissions.


Figure 1: Global population estimates 1950-2015, and projections with 95% prediction intervals, 2015-2100 (from UNPD – World Population Prospects: The 2017 Revision. New York: United Nations Population Division). Currently there are approximately 7.4 billion humans. According to the medium scenario, a population of 10 billion will be reached between 2055 and 2060, and a maximum of over 11 billion by 2100.


A third method – the one that Wynes and Nicholas apply, following Murtaugh & Schlax (2009) – is to distribute a person’s responsibility for a descendant’s emissions proportional to the genetic relatedness to her. In practice, this means that a mother (and likewise, a father) is responsible for her own emissions, half of her children’s emissions, a quarter of her grandchildren’s emissions and so on. The problem with this method is that, if it is to be equally applied to children, it follows that they are responsible for their emissions even though their parents are also responsible for their emissions. In statistics, this is called double-counting, which may lead to corruption of results. To avoid double-counting was also identified as a goal in the Paris agreement from 2015.


A solution: parents are responsible for children’s emissions up to their legal age

My proposal, which avoids double-counting, is to count parents fully responsible for their children’s emissions until they reach legal age. As soon as a person has the right to vote and is of criminal responsibility, she is also fully responsible for her own emissions. (Whether this should be 18 years or younger is up to debate. I presume that the effect would be better if we apply a younger age in order to make young people aware of their responsibility early on.)

This also means that the emissions of the first 18 years of every life are the parents’ responsibility. Thus, a couple with two children would be responsible for the same number of years as if you hold them responsible for all and only their direct emissions. But the effect makes sense: more children mean responsibility for more emissions. This could give people who are concerned about their emissions incentives to reflect on their intentions to have children, or, if they decide to have children, to educate those to live a low-emission lifestyle.

The proposal, I believe, also makes it a less abstract endeavour to deliberate the choice to have children with regards to its carbon consequences than is the case with the proposal of genetic relatedness. A person would not be responsible for her grandchildren’s, or further descendants’ emissions, unless they were born when her child was still underage.

It remains to quantify the emission savings of the decision to have one less child under this proposal, to which I shall turn now.


Can we reduce our carbon footprint by having fewer children?

Suppose you are considering whether to have an (additional) child and are concerned about what this would mean for your carbon footprint. For a very rough calculation, assume that average per capita emissions per year are 5 tons CO2. Per capita emissions of infants may be lower than the average, but 5 tons is a conservative assumption, as emissions in developed countries like the UK are considerably higher. Together with your partner, you would thus share responsibility for 5 additional tons times 18 years, equalling 90 extra tons of CO2. So each parent can be attributed 45 extra tons. This is substantially higher than the lifecycle emissions of a passenger car.3

I am aware that comparing children to cars is provocative. It is meant to show that the emissions of having a child can be meaningfully quantified, just as for many other decisions that individuals make. I acknowledge that there are other reasons for and against a decision to have a child, and its carbon consequences will for many people not be the decisive one. But it remains true that you can substantially reduce your emissions by having fewer children, and this should be commonly known.

In anticipation of possible counterarguments, let me just mention three things. First, my proposal is not meant to, and does by no means imply, that there are trade-offs between the decision to have a child and other lifestyle choices (“since I decided to live childless, my holidays in Australia are consistent with my low-emission lifestyle”). Second, emission trajectories should be included in analyses of future generations’ emissions, which I have neglected here. Let me only repeat that I interpret research on future trajectories as by no means suggesting that we will reach a zero-emission society soon. Third and finally, if everyone were an environmentalist who would refuse to reproduce because of the emission consequences then humanity would go extinct. But not everyone is. There is nothing perplexing about the decision not to reproduce for environmental reasons. The reason for anthropogenic climate change is our lifestyle combined with the fact that we are too many not too few.

By Philippe van Basshuysen

Part 2 →

Philippe van Basshuysen is a PhD candidate in the Department of Philosophy, Logic and Scientific Method at LSE. He works on the question of how institutions such as markets should be designed in order to achieve fair and efficient results. The areas of application include topical issues such as the distribution of refugees, climate and population ethics.



Further reading




[1] CO2e stands for carbon dioxide equivalent, which includes greenhouse gases such as carbon dioxide (CO2), methane (CH4), or nitrous oxide (N2O).

[2] See the IPCC reports for different global socio-economic scenarios and their associated projected emissions. Pretis & Roser (2017) show that there is substantial uncertainty about the scenarios and that they typically underestimated the global emission intensity in the past.

[3] Here is a rough set of assumptions: the EU target for the fleet average to be achieved by all new cars by 2021 is 95 grams CO2/km. Suppose the average distance driven per year is 14,000 km, and that a car is used on average for 11 years. The total CO2 emissions of the use phase of such a car would then equal 14.63 tons. A very rough rule of thumb is that between a third and the full use phase emissions should be added to account for production and disposal phases. Thus, the cradle-to-grave emissions under these assumptions amount to between 20 and 30 tons CO2.”