IN A NUTSHELL Author's NoteAn article which estimates the carbon footprint ethical threshold and the impact of excess emissions on human Life. It is the first of 13 steps in updating the global burden of health inequity based on the recent UN population division trend and prospects
By Juan Garay
Professor of Global Health Equity Ethics and Metrics in Spain (ENS), Mexico (UNAChiapas), and Cuba (ELAM, UCLV, and UNAH)
Co-founder of the Sustainable Health Equity movement
Human Ethical Threshold of CO2 Emissions and Projected Life Lost by Excess Emissions
Since 1850, nearly 2,600 billion metric tons of carbon dioxide (GtCO₂), equivalent to 702 billion tons of carbon, have been emitted into the atmosphere from fossil fuel combustion and land-use changes (1). In 2022, global carbon dioxide emissions from fossil fuels and industry totaled 37.15 billion metric tons (GtCO₂), and these emissions are projected to have risen by 1.1 percent in 2023, reaching a record high of 37.55 GtCO₂ (2).
There is a consensus among scientists that significant dangers will arise if the global mean temperature increases by more than 2 degrees Celsius (3). The relationship between cumulative carbon emissions and global warming indicates that one trillion tons of carbon emissions are linked to a 2-degree Celsius rise. To avoid exceeding this 2-degree increase, we can only emit an additional 300 billion tons of carbon, equivalent to 1,111 billion tons of carbon dioxide.
The United Nations estimates that the global population will grow from 8 billion in 2024 to 10.4 billion by 2100 (4), resulting in the accumulation of 640 billion life years over the remainder of the century. To keep global warming under 2 degrees Celsius during this century (SDG 13.1), the maximum annual average carbon dioxide emissions per person should be 1.73 tons.
If current emission trends continue, global emissions could double to 75 billion tons by 2100 (5), leading to cumulative emissions of 4.26 trillion tons from now until then, which is 3.8 times the remaining carbon dioxide budget. This increase in temperature could result in 218 million excess deaths and a loss of approximately 6,500 million life years, averaging about 30 years lost per excess death (5).
If the 2022 world per capita CO2 emissions (4,72 mT) were maintained during the rest of the century, excessive CO2 emissions would total almost 2 Tn beyond ethical limits. The relation betweem global warming related life years lost (6.5Bn) and excess emissions (2Tn) points at some 1,2 days lost for every excess ton of carbon dioxide emitted annually. At current emission levels and life expectancy this translates to an average of around of one life years lost by EU citizens (5.5 mT pc, 3,8 above the ethical threshold, times 1,2 days and 81,5 years of life expectancy) and three years by those in the US (13mT pc, 11,3 above the ethical threshold, times 1,2 days and 79 years of life expectancy).
The above estimates focus solely on the impact of climate change through temperature increase. However, global warming affects human health in many other ways, such as storms and floods, the disruption of food systems, increases in zoonoses and food-, water-, and vector-borne diseases, population displacements, and mental health issues.
References
(3)https://img.climateinteractive.org/2014/02/A-Trillion-Tons.pdf
(4)https://population.un.org/wpp/
(6)https://www.peah.it/2018/07/5498/
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