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In July 2017, ScienceMag reported on a study:

Eating no meat cuts an individual’s carbon footprint by 820 kilograms of carbon dioxide (CO2) each year [...] by choosing to have one fewer child in their family, a person would trim their carbon footprint by a whopping 58.6 metric tons

http://carbonindependent.org/22.html gives

1/4 tonne CO2 equivalent per hour flying.

Are these figures accurate?

Gnubie
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  • There seems to be two different claims challenged in the question, one about children and one about flying. You should rather pick one of them and propose the other one in another question. – Evargalo Jul 08 '19 at 12:36
  • Aren't you comparing oranges to apples? If you assume your life expectancy is X years and sum not eating meat for the rest of your life, the two figures aren't that different if you're in your early 20s. – Denis de Bernardy Jul 10 '19 at 13:47
  • Philippe van Basshuysen and Eric Brandstedt published on 26 March 2018 http://iopscience.iop.org/article/10.1088/1748-9326/aab213 "we have argued that the attribution of responsibility Wynes and Nicholas invoke involves a kind of multiple counting which runs counter to the objectives of the study." – Gnubie Oct 21 '21 at 20:53

2 Answers2

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To come up with the emission per child, the original source Reproduction and the carbon legacies of individuals Global Environmental Change Volume 19, Issue 1, February 2009, pages 14-20, is considering an infinite series.

In other words, having one child results in all the lifetime emission of said child, plus all that child's descendants' emissions. Since each child usually has two biological parents, 4 grandparents, etc., to avoid double counting, the reference weights descendants' emissions by 0.5^n, where "n" is the number of generations into the future. For example n=1 for children, n=2 for grandchildren, etc.

This infinite series is potentially divergent, if fertility rates are above 2. So the reference assumes that the fertility rate will drop to 1.85 everywhere in the world by 2050, permitting the series to be convergent.

DavePhD
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  • Thanks, @DavePhD. Is that per parent? E.g. if my partner and I both have a child, would both of us incur the 58.6 tonnes? – Gnubie Jun 13 '19 at 11:42
  • @Gnubie Yes, 58.6 tons per year for the mother and another 58.6 tons per year for the father according to the journal article associated with the original question https://iopscience.iop.org/article/10.1088/1748-9326/aa7541/meta#erlaa7541r39, which cites to the source in this answer. – DavePhD Jun 13 '19 at 15:46
  • If this is the sum of the series, how can it give a result of 58.6 tons *per year* ? Isn't it 58.6 tons *overall* ? – Evargalo Jul 08 '19 at 12:35
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    @Evargalo the sum is much more than 58.6 tons. "Under current conditions in the United States, for example, each child adds about 9441 metric tons of carbon dioxide to the carbon legacy of an average female". So by dividing by the initial person's lifetime, it is annualized. (plus there are two parents each half-responsible and each country is different) – DavePhD Jul 08 '19 at 14:03
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    What do you mean "usually has two biological parents". Isn't that a hard requirement? Even with artificial insemination, there is still a donor that existed. We don't yet have artificial sperm or a uterus, and I don't believe there are cases of hermaphrodites self-impregnating. – Brian R Jul 08 '19 at 16:20
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    @BrianR https://www.nature.com/news/genetic-details-of-controversial-three-parent-baby-revealed-1.21761 – DavePhD Jul 08 '19 at 16:56
  • @DavePhD - That's an interesting edge case, thank you. It makes us consider what the impact of the mitochondrial DNA would be on the calculations posted in this answer. – Brian R Jul 08 '19 at 17:00
  • Formally speaking, you don't actually need the sum to be convergent. There is a finite amount of time in which the problem is relevant, so a finite number of potential generations to account for. It's not difficult to write down a value for a finite geometric sum; convergence just makes it easy to work independently of the number of generations and largely ignore deviations in late generations. And you can pretty easily come up with an upper bound on the conceivable number of generations (be ridiculous and suppose a new one every 12 years over a few billion years and there you go), too. – zibadawa timmy Jul 11 '19 at 06:43
  • @zibadawatimmy I agree, but the reference as far as I understand simulates births and keeps adding until humans no longer exist due to the 1.85 fertility rate and the fact that fractional numbers of children aren't possible. – DavePhD Jul 11 '19 at 10:58
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The answer is yes, using world average variables and a mandatory time frame of 71 years, one's average lifetime, fertility 2.4, carbon footprint 4, 1st birth at 26):

104 people need to go vegetarian to lesser carbon emissions by 837 which is the additional emission of 1 child, including her child, all non vegetarian, over 71 years. Average values used, calculations have been done but deleted by the moderator(Sklivvz).

The above assumes that child and all ancestors up to 71 years forward will not be vegetarians. If all are, footprint drops to 558 and 69 people need to go vegetarian, which is as close to 71 as statistical mistake.

Sources used: Initial quastion's https://www.sciencemag.org/news/2017/07/best-way-reduce-your-carbon-footprint-one-government-isn-t-telling-you-about

Carbon footprint calculator: https://www.carbonfootprint.com/calculator.aspx

Average fertility 2018 https://www.google.com/search?q=world+average+fertility+rate+2018&rlz=1C1GGRV_enGR751GR751&oq=wolrds+average+fert&aqs=chrome.2.69i57j0l5.6879j0j8&sourceid=chrome&ie=UTF-8

Average 1st birth age https://www.google.com/search?q=world+average+birth+age&rlz=1C1GGRV_enGR751GR751&oq=world+average+birth+age&aqs=chrome..69i57j0.24046j0j8&sourceid=chrome&ie=UTF-8

Vegetarian less footprint https://www.vox.com/2014/7/2/5865109/study-going-vegetarian-could-cut-your-food-carbon-footprint-in-half

Stefanos Zilellis
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