Addendum: age-specific carbon budgets

(There has been an important update on the Remaining Carbon Budget in this paper by Piers Forster et al. It reduces the RCB significantly, and thus the numbers used in this piece. See the note the end for more detail).

This is the third in a series of blogs about personal carbon budgets. In the first, I made the case for personal carbon budgeting and made proposals for improvements to budget calculators currently available. In the second, I suggested what a personal lifetime budget could be for someone born today. This third one extends the analysis to offer an age-specific calculator which takes life expectancy into account.

The carbon bit is derived from the earlier analysis: a global average of 1.4 t CO2e per person per annum to limit warming to 1.5 degrees, 2.9 for 2 degrees. The age-specific bit is slightly more complicated, because it requires information about life expectancy at different ages. So, if you are 30 now, your carbon budget depends on how many years you are going to live.

As before, I have worked with global averages, and in this case, have not differentiated between men and women. Women, of course, live longer, so the ratio of men to women (which is above 1 in the first half of life), falls sharply as people get older. The life expectancy tables are derived from WHO data, which provide information about the remaining years of life. Our 30 year old has 47 years left, a 70-year old just 15. Note that these numbers are slightly more generous than global life expectancy at birth, which is currently 73. That is because mortality falls before it rises as people age: infant and child mortality or deaths in childbirth get stripped out, and by the time you get to 70,  you are unlikely to die of childhood diseases or of giving birth.

The data are appended, and the results are as follows, first as a table, then as a graph. Note these are global average numbers, not gender differentiated. From the data in the Appendix, women would have a slightly larger budget at each age.

Table 1

Personal budget for different degrees of warming (t CO2e)

Figure 1

I don’t pretend that these data are more than simple approximations. It would be possible to disaggregate by gender and by country, where data are available. No account is taken of distribution effects as between countries.

The point, though, is to focus on the choices we make as individuals, and on the pressure we need to exert for system change. Personally, knowing how few tons I have left to ‘spend’ certainly concentrates the mind.

P.S. Carbon Brief had some useful work on lifetime budgets, back in 2019: https://www.carbonbrief.org/analysis-why-children-must-emit-eight-times-less-co2-than-their-grandparents/.

Appendix

Years remaining by age group (global average)

Years remaining data from WHO: https://www.who.int/data/gho/data/themes/mortality-and-global-health-estimates/ghe-life-expectancy-and-healthy-life-expectancy

Sex ratio data from: https://statisticstimes.com/demographics/world-sex-ratio.php#:~:text=With%20106.6%20boys%20per%20100,81.8%20for%20those%20over%2065

Update (June 2023)

 This update uses the latest data on the Remaining Carbon budget, from Forster et al, in this paper. The RCB data and the recalculation of the personal lifetime carbon budget are in this companion piece. Using the same assumptions as in the main text, the lifetime budget has fallen

•  100 tons of GHGs (for 1.5 degrees); and
•  200 tons of GHGs for 2 degrees.

to a lifetime budget of only

• 55 Gt for 1.5 degrees; and 
• 190 Gt for 2 degrees

The table and graph can then be amended as follows:

Personal budget for different degrees of warming: