A new study has quantified the impact of adding one ton of carbon dioxide emissions from humans on human mortality. This is a Peruvian Amazon farmer setting ablaze to clear the land for agriculture. These fires are a significant source of greenhouse gases. Credit: Kevin Krajick/Earth InstituteA new measure, the "mortality price of carbon," has been published in a study. This is how many lives are lost or saved depending on whether our carbon emissions increase or decrease. They are very high if the numbers hold. Today's study was published in Nature Communications.R. Daniel Bressler is a Columbia University Ph.D. Candidat. He saw a significant gap in current estimates of social cost of carbon. This dollar figure economists assign to each ton of carbon based on the future damage it will cause. The social cost of carbon is a complex and flexible number that underpins the way governments around the world formulate climate policies. It suggests how much we should pay today to prevent future damages. Recent studies show that climate change will lead to millions of premature deaths. However, current estimates for the social cost of carbon are based on old research, which does not include these projections. Bressler tries to include the new data.Bressler says, "Based on the decisions made either by individuals or businesses, this tells how many lives will be saved or lost." It quantifies the mortality consequences of these decisions. This brings the question down to an easier-to-understand level.First, some caveats. Bressler does not claim that his number is final. Bressler used several public-health studies to estimate the impact of climate change on mortality. There is much uncertainty in these studies, so Bressler's main conclusions are based only on their central estimates. Bressler's study does not account for heat-related deaths, but only direct temperatures. It also excludes possible deaths due to storms, floods or crop failures. This is a widely known threat, but it is harder to quantify. His estimate may in fact be "a great underestimate," he admits.Assuming that the emissions are continuing to rise on their current high trajectory, he calculated a number of 2.2610-4 or 0.000226 extra deaths per metric ton of CO2 emitted above the current rate.Bressler struggled to understand what this number meant so he came up with another way. This means that for every 4,434 tonnes of CO2 we add above the 2020 emission rate, one person will die. These 4,434 tons is equivalent to the lifetime CO2 emissions of 3.5 Americans. Or, to put it more personally, adding the lifetime CO2 emissions of one American to our current trajectory would theoretically result in 0.29 additional deaths. This does not mean that every living American will be able to kill 0.29 million people. It simply means that 1,276 metric tonnes of carbon dioxide tons of carbon would cause 0.29 deaths per century due to temperature-related mortality.This is a very low number compared to the majority of the rest of the planet. Globally, the average global emission of 4,434 tons is equivalent to 12.8 people's lifetime (theoretically, only 0.08 people per person). It would take 9.4 people to emit the same amount of emissions in the United Kingdom (which is relatively wealthy) to cause the same excess mortality (0.11 per capita). It would take 25.8 Brazilians (0.04 per capita) or 146.2 Nigerians (0.01 per capita). Only a few countries are worse than the United States, such as oil-intensive Saudi Arabia (which kills 0.33 per capita). This list also includes Australia, Qatar and Kuwait, as well as the United Arab Emirates.To put it in a more personal way, adding 1,000,000 metric tons to 2020's baseline emissions would result in 226 deaths. These 1 million tons are equivalent to 216,000 passenger cars, or 35 commercial aircraftliners, or 0.24 coal-fired electricity plants.One human death is possible by adding 4,434 tonnes of carbon dioxide to the global emissions above the 2020 baseline rate. The lower bars in this chart indicate that individuals from each country would have a greater impact. These 4,434 tons of carbon dioxide are equivalent to the lifetime emission of just 3.5 Americans. This is in contrast to the 15.6 Mexicans and 146.2 Nigerians. Credit: Adapted by Bressler, Nature Communications 2021According to the study, if we continue on our current emissions trajectory, 2050 will see average temperatures rise by 2.1 degrees Celsius (3.8 F) over preindustrial times. This is the limit that will trigger the worst effects of climate change. Things would quickly get worse, with temperatures rising to 4.1 degrees Celsius (7.4 F) by 2100. Bressler predicts that climate change will cause an additional 83 million deaths in this scenario by 2100.This scenario would see temperatures reaching dangerously high levels by 2050, so most premature deaths would occur after that date. Although the study doesn't explicitly consider geographic distribution, Bressler states that the majority of deaths would occur in the regions already experiencing the highest temperatures and the poorest living conditions: Africa, South Asia, and the Mideast.What does this mean for the social cost of carbon? It skyrockets if you accept the numbers of the study.The social cost of carbon, which was first proposed by William Nordhaus, a Nobel-prize-winning economist, in the 1990s has seen many changes. This is due to increasing knowledge about the human effects of climate change and shifting predictions of future temperatures, as well as the extent to which we can adapt to them. There are many ways to combine all these factors into one monetary figure.Bressler uses Nordhaus's DICE model, which Bressler expands on. It currently places the 2020 social cost for carbon at $37 per ton. This model suggests that to strike the best balance between climate-related damage and costs of cutting emissions, we should stop producing them now and reduce them gradually over time, starting in 2050. This would lead to a warming of 3.4 degrees Celsius (6.1 F) by 2100.Bressler adds mortality to the model and puts the figure at $258 per tons. This means that we need to reduce emissions immediately and achieve full decarbonization by 2050. This would result in only 2.4 degrees of global warming by 2100. According to Bressler's calculations, the number of excess deaths would fall to 9 million by 2100, a savings of 74 millions lives. He says that this is not a recommendation for the optimal climate strategy.These figures can be manipulated politically. The Obama administration mandated in 2009 that scientists calculate the U.S. carbon cost. By 2017, it was $52. Trump's administration stopped all scientific work regarding the question and came up with estimates that ranged from $15 to $1 per ton. The scientists were reassembled after Joseph Biden was elected. A February interim report showed that the 2020 price had risen to $51 per tonne. An official estimate will be available by January 2022.Bressler states, "My opinion is that people shouldn’t take their per-person mortalities too personally." "Our emissions are a function technology and culture in the places we live." He says that individuals, businesses, and communities can all work together to reduce their emissions. He says that a larger-scale policy, such as carbon pricing, cap-and-trade, and investments into low-carbon technologies, and energy storage, is a better solution.
