A metric of mortality
A measure of the mortality cost of carbon (MCC) has been
proposed by Bressler (2021), who describes it as a metric for “calculating the
marginal mortality effects of emissions.” The metric “represents the number of
excess deaths over some time period from one ton of additional
carbon-dioxide-equivalent emissions.” Its value depends on the time period
chosen for the calculation, and upon predicted changes in global average
temperatures, which are themselves dependent on global emissions. The metric
makes it possible to calculate, for example, the number additional of tons of
carbon dioxide emitted in 2020 which would result in one excess death in the
years 2020 to 2100. Such information, along with other measures, “can be useful
in informing the decision-making of individuals” and organisations “in
determining the social impact of the emissions generated by their activities”
as well as guiding policy at higher levels.
An insight at the individual level can be provided by
estimating the number of excess deaths predicted to result from one person’s
lifetime carbon emissions (treated as if all emitted in 2020). This number
varies from country to country, since lifetime emissions also vary with
location, but it is, unsurprisingly, highest in the rich developed nations.
Bressler draws on three main sources in developing the mortality
cost of carbon, The Lancet Planetary Health study (Gasparrini et al., 2017),
the World Health Organization study (Hales, et al., 2014) and 2019 Climate
Impact Lab study (Carleton et al. 2020). The limitations of these studies in
providing the evidence needed to support the MCC are discussed in some detail,
but they “came sufficiently close” to meeting the ideal criteria. The studies
provided Bressler with data on the “increase in the mortality rate under
different warming scenarios”. For a given increase in global temperature, more
excess deaths are expected in those regions which are at present hotter than
average, and some colder places will have fewer excess deaths. The effects of
some factors, such as conflicts arising from climate change, have been ignored
due to lack of evidence.
Figures for the MCC are given with different levels of
uncertainty: a central estimate is that “reducing … emissions by 1 million
metric tons of carbon dioxide in 2020 saves 226 lives … in expectation from 2020 to 2100”. (This
quantity of carbon dioxide would typically be emitted in a year by “35
commercial airliners, 216,000 passenger vehicles, and 115,000 homes in the
United States.”)
While from some viewpoints it may be considered wrong
ever to put a monetary value on a human life, decision makers may find
themselves forced to ask how much a life is worth, and how much it costs to
prevent carbon dioxide emissions. Bressler notes that some methodologies value lives
in richer countries more than lives in poorer countries, and avoids this issue
by using the global average value of a statistical life year, taken as “just
under $12,000 in 2020.” UN projections for current world life expectancy are
between 72 and 73 years (Macrotrends 2021), resulting in a life value of about
$850,000.
Methods of modelling climate change and its effects are
central to the study, and Bressler refers to Integrated Assessment Models
(IAMs), the Social Cost of Carbon (SCC), and the Dynamic Integrated model of
Climate and the Economy (DICE). Integrated Assessment Models “are used to
answer central questions about climate change, from how the world could avoid
1.5C of global warming at the lowest cost, through to the implications of
countries’ current pledges to cut emissions” (Carbon Brief, 2018). The Social
Cost of Carbon “tries to add up all the quantifiable costs and benefits of
emitting one additional tonne of CO2, in monetary terms. This value can then be
used to weigh the benefits of reduced warming against the costs of cutting
emissions” (Carbon Brief, 2017). The Dynamic Integrated model of Climate and
the Economy is the IAM used by Bressler in his study, and he refers to two
versions, DICE 2016 and DICE-EMR. An example of the use of a DICE model is
given by Nordhaus (2017) in his study on the social cost of carbon, which
presented “updated estimates based on a revised DICE model” and estimated that the
social cost of carbon (SCC) “is $31 per ton of CO2 in 2010 US$ for the current
period (2015).”
Bressler notes that integrated assessment models used to
set a social cost of carbon do not adequately take into account the impacts of
human mortality. He uses the results of DICE-2016 as his baseline,
and modifies the model to take better account of temperature-related mortality,
referring to the modified IAM as DICE-EMR (Dynamic Integrated Climate-Economy
Model with an Endogenous Mortality Response). One effect is to increase the “2020
SCC from $37 to $258 … per metric ton in the baseline emissions scenario.”
Another effect of “pursuing the DICE-EMR optimal emissions path” is to reduce
mortality, saving “a projected 74 million lives over the course of the
twenty-first century ... as the number of temperature-related excess deaths
falls from 83 million in the DICE baseline emissions scenario to 9 million in
the DICE-EMR optimal emissions scenario”. The lower mortality corresponds to
the lower global temperatures associated with the DICE-EMR path and its higher
SCC.
In a supplement to his main article (The Mortality Cost
of Carbon – Supplementary Materials) Bressler addresses the effect of extending
his analysis beyond 2100. The time scale is extended to 2500, and projections
of cumulative excess global deaths are given. Two scenarios are described; in
the first (the DICE baseline scenario) annual climate related deaths peak in
2240 at about 19 million, falling below 10 million per annum in 2500, and
totalling more than 5000 million by 2500. In the second (DICE-EMR optimal)
cumulative excess global deaths reach a maximum of about 100 million.
References
Bressler, R.D., 2021, The mortality cost of carbon, Nature Communications, online, accessed
22 Oct 2021
https://www.nature.com/articles/s41467-021-24487-w
Carbon Brief, 2017, Q&A: The social cost of carbon,
online,
accessed 29 Oct 2021
https://www.carbonbrief.org/qa-social-cost-carbon
Carbon Brief, 2018, Q&A: How ‘integrated assessment
models’ are used to study climate change, online, accessed 29 Oct 2021
https://www.carbonbrief.org/qa-how-integrated-assessment-models-are-used-to-study-climate-change
Carleton, T. et al. 2020, Valuing the Global Mortality
Consequences of Climate Change Accounting for Adaptation Costs and Benefits,
National Bureau of Economic Research, online, accessed 28 October 2021
https://www.nber.org/papers/w27599
Gasparrini, A. et al., 2017, Projections of
temperature-related excess mortality under climate change scenarios, The Lancet Planetary Health 1,
e360–e367, online, accessed 28 October 2021
https://www.sciencedirect.com/science/article/pii/S2542519617301560
Hales, S. et al., 2014, Quantitative risk assessment of
the effects of climate change on selected causes of death, 2030s and 2050s, World
Health Organization, online, accessed 28 October 2021
https://apps.who.int/iris/bitstream/handle/10665/134014/9789241507691_eng.pdf
Macrotrends, 2021, World Life Expectancy 1950-2021, online,
accessed 28 October 2021
https://www.macrotrends.net/countries/WLD/world/life-expectancy
Nordhaus, W.D., 2017, Revisiting the social cost of
carbon, PNAS, online, accessed 28
October 2021
Comments
Post a Comment