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More Carbon Will Kill More People, Find Out How Many

A new metric, dubbed as the “mortality cost of carbon,” factors in the latest data on climate change to predict future climate-related deaths, redefining our current understanding of the social cost of carbon.

Scientists often calculate the environmental cost of carbon emissions, but what about their social cost? In a new study published in Nature Communications, a researcher from Columbia University has coined a new metric that allows us to calculate how many future lives will be lost or saved if our current carbon emissions were to increase or decrease. The new metric, dubbed as the “mortality cost of carbon” predicts a bleak future with many lives to be lost should current levels of emissions continue to persist.

Up until recently, the social cost of carbon has been largely estimated in terms of economic loss, with many economists attaching dollar figures to each ton of emissions to represent the price of future carbon damage. While this method has been effective so far in helping governments worldwide to gauge the extent of carbon destruction and plan climate-related policies, monetary figures are complex, highly malleable, and prone to fluctuations. Moreover, present approximates of the social cost of carbon rely on outdated studies that fail to factor in new reports about the effects of climate change that is projected to cause millions of premature deaths.

Noticing this gap, R. Daniel Bressler, a doctoral student at Columbia University’s Earth Institute and the university’s School of Public and International Affairs, took the opportunity to add in the new data by creating a new indicator to evaluate the cost of carbon emissions.

“Based on the decisions made by individuals, businesses, or governments, this tells you how many lives will be lost, or saved,” explained Bressler. “It quantifies the mortality impact of those decisions. It brings this question down to a more personal, understandable level.”

Assuming that emissions continue to rise following their current trajectory, Bressler calculated that for every 4,434 metric tons of carbon dioxide that we add beyond the 2020 baseline rate of emissions, we will kill one person. Although 4,434 tons might seem large, he noted that it translates to the amount of emissions produced by 3.5 Americans throughout their lifetime. In other words, if we proceed on our current path, adding the current lifetime emissions of one American would, in theory, kill 0.29 extra humans.

On a global scale, 4,434 tons equals the lifetime emissions of 12.8 people, thus bringing the death toll to 0.08 people per capita. In bigger, less personal terms, adding 1 million metric tons to the 2020 baseline emissions would kill 226 people. 1 million metric tonnes are equivalent to the annual emissions of 216,000 passenger vehicles, or 115,000 homes, or 35 commercial airlines, or 0.24 coal-fired power plants.

The study also predicted that by 2050, we will see a 2.1 degree Celsius increase in average global temperature, after which the worse consequences of climate change will start to kick in. Temperatures will increase by 4.1 degrees Celsius, leading to 83 million excess deaths by 2100. Most of these deaths, according to Bressler, would be observed in regions that are already the hottest and poorest, like in Africa, the Mideast, and South Asia. Many more findings were reported in the study. But what exactly do these figures mean for our present understanding and future predictions of the social cost of carbon?

The most commonly used model to estimate the social cost of carbon, the DICE model by economist William Nordhaus, placed the 2020 social cost of carbon at $37 per metric ton. The framework suggests that to achieve the optimal balance between climate-related damages and the costs of cutting emissions, we should plateau emissions now and cut gradually starting in 2050. Doing this would theoretically result in 3.4 degrees Celsius of warming by 2100.

However, with Bressler’s new model that factors in mortality, the social cost of carbon is raised to $258 per ton–seven times more than the initial $37. This suggests that cutting down emissions can no longer wait until 2050. Instead, full decarbonisation should be achieved by 2050. And if successful, the future generation can look forward to only 2.4 degrees Celsius of warming and 9 million excess deaths by 2100 – a stark drop from the initial prediction of 83 million, effectively saving 74 million lives.

With these new figures, Bressler emphasised that the projections are not necessarily a prescription for the optimal climate policy, but merely an update to the DICE model. Bressler also acknowledged that there are several limitations to his new metric. Although he gauged the mortality impact of climate change based on the central estimates of several key public-health research, those studies were riddled with a number of uncertainties.

Additionally, Bressler’s study only accounts for mortality that is directly related to temperature like heat stroke. The “mortality cost of carbon” does not take into account other possible deaths from storms, floods, crop failures, infectious diseases, and wars because said factors were much more difficult to quantify. Therefore, Bressler considers his calculations to still “be a vast underestimate” and believes that the findings of his study should be taken with a grain of salt, both on a policy and personal level.

“My view is that people shouldn’t take their per-person mortality emissions too personally. Our emissions are very much a function of the technology and culture of the place we live,” said Bressler. Although individuals, companies, and communities should try to curb their own emissions, a more effective solution would be “large-scale policies such as carbon pricing, cap and trade, investments in low-carbon technologies and energy storage.” [APBN]

Source: Bressler, R.D. (2021). The mortality cost of carbon. Nature Communications, 12, 4467.