This is a quick response to a question about a ‘carbon budget for life’ (Rosalind Readhead – Twitter 11th Jan 2021; thread at: https://twitter.com/Privatecarfree/status/1348566487766888449)
A Personal Annual Carbon Budget
Working from the UK carbon budget in our recent paper (A Factor of Two ) it would be possible to estimate an annual and reducing carbon budget per person for people in the UK, based on the emissions pathway that accompanies the budget.
But, should such a carbon budget be divided between: 1) all people in the UK (from infant to adult); 2) just among adults (at what age?); 3) per UK household; or 4) is there another more appropriate division?
A Personal Carbon Budget for Life
To estimate a budget for life would be far more complicated and require some very clear assumptions to be made; for example:
Should a 98-year-old get the same remaining carbon for life budget as a ten-year-old?
Should a 16-year-old in 2021 get the same budget as a 16-year-old in 2037?
One way around this may be to use forecasts of population growth and calculate the person/years each year out to say 2040, by when UK CO2 emissions from energy need to be zero (assuming we follow a rapid mitigation pathway starting now). Then, based on mean life expectancy for people of different ages, a remaining carbon budget for life could be estimated. This would then permit a carbon budget for life to be derived for people of different ages from now out to 2040 (i.e. the sum of the person/year budget for each year along the annually declining emissions pathway).
A 1-year-old child in 2021, would have a ‘large’ remaining budget (very likely to live to 2040)
A 50-year-old adult in 2021 would have a ‘moderate’ remaining budget (likely to live to 2040)
A 98-year-old adult in 2021 would have a small remaining budget (unlikely to live to 2040)
For each new baby born, a remaining budget for life could be allocated based on the mean probability of that baby still being alive for each year out to 2040, by when there would be no more UK carbon budget remaining.
In my view, of the two options, a declining annual carbon budget per adult, and based on an emissions pathway that matches the UK’s fair carbon budget for 1.5-2°C (at chosen probabilities/chances of success), would make more sense than a ‘for life’ carbon budget. Tyndall Manchester did some work on a version of this back in 2005 – Domestic Tradable Quotas .
As a quantitative guide: emissions from energy in 2020 were around 7 tonnes of CO2 per adult (18 years and older) – this is very approximately 10% lower than in 2019. From the start of 2021 these emissions would need to continue to reduce at a minimum of 10% year on year if the UK is not to renege on its Paris commitments. It is important to note this is for territorial emissions only, but does include aviation and shipping emissions. As a (pre-Covid) guide, around 4.5 tonnes (~60%) of energy emissions arose from the direct use of energy by individuals. These comprised, on average (and very approximately): 2 tonnes for private car travel; 0.5 tonnes non-business aviation; 1.5 tonnes domestic heating (including hot water and cooking); 0.5 tonnes domestic electricity use.
To reiterate, the above values are average levels of emissions, and at a 10% per year cut, if imposed across all adults, would rapidly bring a stark reality to bear on the lifestyles of high-emitting individuals (e.g. policy makers, climate scientists, journalists, barristers, entrepreneurs, et al). Put another way, if the UK’s equitable contribution to the Paris 1.5-2°C commitment was fairly distributed amongst UK citizens, there would be an overnight sea change in the lukewarm response to the much heralded climate emergency. Real zero by 2035-40 is a completely different agenda to net-zero by 2050.
 A Factor of Two: https://www.tandfonline.com/doi/pdf/10.1080/14693062.2020.1728209
 Domestic Tradable Quotas: https://www.researchgate.net/publication/237228029_Domestic_Tradable_Quotas_A_policy_instrument_for_reducing_greenhouse_gas_emissions_from_energy_use