Adding projected heat-related deaths into cost-benefit analysis of federal rules would tilt policymaking in favor of more aggressive carbon emissions cuts, a new study finds.

Why it matters: The social cost of carbon helps determine the outcome of cost-benefit analyses that underpin federal regulations. Adding in global warming's potential to cause more heat-related fatalities would tilt the policy calculus from supporting a gradual phaseout of emissions starting in 2050, to fully decarbonizing by the same year.

The big picture: The study, published Thursday in Nature Communications, adds temperature-related mortality impacts into calculations of the estimated damage to society caused by the emission of one addition metric ton of carbon dioxide.

• Recent studies have shown that climate change will likely cause millions of premature deaths worldwide, primarily through increased heat waves and other disasters like floods, more severe hurricanes, food shortages and other effects.
• R. Daniel Bressler, a doctoral candidate at Columbia University's Earth Institute, found that that by taking direct heat-related deaths into account, the more appropriate social cost -- expressed as a "mortality cost of carbon," is surprisingly steep.

By the numbers: Bressler determined that the mortality cost of carbon works out to 0.000226 excess deaths through 2100 per metric ton of carbon dioxide emitted.

• That sounded to him to be infinitesimally small and hard to grasp, so he did further calculations.
• Every 4,434 metric tons of CO2 added to the atmosphere in 2020 causes one death through 2100, the study found. This is equivalent to the lifetime emissions of 3.5 average Americans, given their high per capita emissions rates, or 146.2 Nigerians, considering the lower per capita emissions rates in that country.

Details: Bressler also added the mortality cost of carbon to the well-known Dymamic Integrated Climate-Economy Model, or DICE, which Nobel Prize-winning Yale environmental economist William Nordhaus pioneered.

• In doing so, Bressler found that the social cost of carbon as calculated by the updated DICE model would increase seven-fold, from $37 per metric ton to $258 per metric ton.
• Bressler also found that in a business as usual emissions scenario, there would be 83 million projected cumulative excess heat-related deaths between 2020 and 2100 using according to the modified DICE model.
• However, fully decarbonizing by 2050 would slash that total to just 9 million excess deaths, Bressler told Axios.
• "The big picture is just that, there are a lot of lives that can be saved from reducing emissions," Bressler said. The study, for example, shows that taking one coal-fired power plant offline in the U.S. in 2020 would, through the end of the century, prevent 904 deaths.
• Bressler noted the fatality figures are probably an underestimate, because the study ignores all other climate-related causes of death in addition to heat.

Yes, but: There are a number of uncertainties in the new study, including that the climate mortality projections themselves vary considerably in their results. Bressler tried to account for that by including central estimates, rather than the high or low ends of the spectrum.

• The study also doesn't factor in the co-benefits of shutting down certain types of fossil fuel power plants, which produce other harmful air pollutants in addition to greenhouse gases.
• "That's something that, if you added it into the model, you would also see, probably even stricter climate policy," Bressler said.