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 1,778 billion metric tons of carbon dioxide (GtCO₂), equivalent to 478 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), yet many feed-back negative effects will start with 1.5 degrees warming. The relationship between cumulative carbon emissions and global warming indicates that 2.8 Tn of human cumulative CO2 emissions are linked to a 2-degree Celsius rise and 2 Tn with 1.5 . To avoid exceeding 2 degrees we can only emit an additional 991 Bn tons of carbon dioxide, 241 for 1.5. At current global annual emission rate (37 Bn Tn in 2023), we will hit 2 degree warming by 2050, and 1.5 by 2030. (4)
The United Nations has recently estimated that the global population will grow from 8 billion in 2024 to 10,1804 billion by 2100 (5), resulting in the accumulation of 765 billion life years over the remainder of the century. We estimate the ethical threshold pc by dividing the remaining carbon budget between the human life years in the remainder of the century. To keep global warming under 2 degrees Celsius during this century, the maximum annual average carbon dioxide emissions per person should be 1,3 tons, and to limit it to 1.5, just 0,3 tons.
If the 2022 world per capita CO2 emissions (4,63 mT) were maintained during the rest of the century, excessive CO2 emissions would total almost 1,615 Tn beyond ethical limits and global warming would exceed 8 degrees. Such global warming, the highest in 50m years, would result in 218 million excess deaths and a loss of approximately 6,500 million life years, averaging about 30 years lost per excess death (6).
The relation between excess emissions and the consequence of life years lost (6.5Bn) results in some 1,46 days lost for every excess ton of carbon dioxide emitted annually. At current emission and life expectancy levels this translates to an average of around of 450 life days (1,2 years) lost by EU citizens on o (5.5 mT pc, 3,8 above the ethical threshold, times 1,46 days and 81,5 years of life expectancy) and 1300 days (3.5 years) by those in the US (13mT pc, 11,3 above the ethical threshold, times 1462 days and 79 years of life expectancy) mainly to those living in low-CO2 emission countries.
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
1) https://doi.org/10.5194/essd-15-5301-2023
(3)https://img.climateinteractive.org/2014/02/A-Trillion-Tons.pdf
(4)https://www.mcc-berlin.net/en/research/co2-budget.html
(5)https://population.un.org/wpp/
(6)https://www.peah.it/2018/07/5498/
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