Study puts a price on climate-driven death

A new study suggests the United States is undercounting the cost of additional deaths caused by climate change — a finding that could spur governments to do more to reduce carbon emissions.

The study published in Nature Communications advances the idea of “the social cost of carbon,” which combines the market cost of carbon dioxide with “non-market” costs, such as rising sea levels and fatalities from higher global temperatures.

The Obama administration estimated the social cost of carbon to be about $50 a ton, but the paper published Thursday suggests a much higher total that could reach up to $258 per ton.

Such figures would also dwarf the market costs of carbon, which currently trade in the European Union around $53 per ton.

The difference comes from adding what study author R. Daniel Bressler calls “the mortality cost of carbon.”

“The question is, how many excess deaths do you get when you increase emissions by some amount,” Bressler, a Ph.D. candidate at Columbia University, told The Hill.

If emissions continue unabated, his model found, 75 million additional people will die from heat-related causes who would otherwise survive if the world reaches net zero by 2050.

The model also helps put the social costs of carbon into perspective.

By factoring in more recent research on the effects of climate change into the leading model for assessing carbon costs, Bressler came up with far higher numbers: at the high end, $258 per ton, which assumes that emissions continue at their current rate. That’s more than five times the price being considered by the Biden administration, and a far stronger policy impetus for cutting carbon emissions.

Based on Bressler’s model, a power plant that produces a million tons of carbon dioxide for a single year would lead to 226 excess deaths over the next 80 years. 

On a smaller scale, the lifetime emissions of every 3.5 Americans — slightly over the size of the average family — would kill one additional person worldwide over the next 80 years, though this is more a metric of how carbon-intensive existing U.S. infrastructure and lifestyles are than a result of individual choice. 

In far-poorer Nigeria, for comparison, Bressler found that it would take the emissions of nearly 150 people to reach one additional death, or nearly 13 people emitting at the global average. 

This discrepancy gives grim emphasis to the demand made by India at last week’s Group of 20 meeting for wealthier countries to cut their per-capita carbon emissions to at least the global average by 2030, according to the Hindustan Times.

Bressler’s study attempts to unravel a key problem with the social cost of carbon that was identified in a 2017 report by the National Academy of Sciences (NAS). The NAS report critiqued the fact that the social cost of carbon is typically presented as a single price, like the Obama administration’s $50.

That leaves policymakers little transparency about either the actual quantities of the individual factors that go into that single number — such as excess deaths or sea level rise — or the price that economists have assigned to it.

And because the social cost of carbon is largely based on the impacts of carbon emissions on future generations, it requires economists to decide the degree of generational damage they could accept — a consideration as much moral or ethical as it is scientific.

That’s why the NAS called for scientists and economists to work to “disaggregate” the social cost of carbon by breaking it apart into its component parts so that policymakers would have clearer numbers to work with. 

In addition to breaking impacts down by sector, the NAS report suggested they do so by giving impacts not only in price but also in “natural numbers” — which for mortality is, of course, number of deaths.  

When Bressler factored mortality into the social cost of carbon, he ended up with a number that was far higher than the one delivered by one of the concept’s key pioneers. Nobel laureate William Nordhaus, in a 2017 paper in PNAS, set the price at $31.

Nordhaus’s model remains the industry standard. The Dynamic Integrated Climate-Economy model (DICE) was introduced in 1994 and won him the Nobel Prize for economics in 2018.

That is relevant because based on those prices as compared to the cost of getting off carbon fuels, Nordhaus calculated that the optimal strategy was for carbon emissions to plateau by mid-century, then slowly decline.

“I’m definitely standing on the shoulders of his work,” Bressler said. The DICE formula makes up the skeleton of his model, but he believes his focus on mortality significantly updates Nordhaus’s $31 figure. 

The risks associated with climate change are far more dire than thought in 2017 — a fact Nordhaus acknowledged in his 2018 Nobel acceptance speech, when he recommended that governments reassess the social cost of carbon each year.

The last four years haven’t just changed economists’ estimates of the costs of carbon, they have also driven those costs up. That’s because the impacts of carbon emissions are nonlinear, Bressler noted. Every additional ton of carbon released, or fraction of a degree of global heating, inflicts more damage than the one that comes before.

“As you get toward 3 or 4 degrees Celsius of warming, you cause a significant number of excess deaths,” Bressler said, noting the graph of additional mortality becomes a steep exponential curve — what economists call “convex.” 

In other words, if temperatures have already risen 3.5 degrees Celsius, an additional tenth of a degree will be far more deadly — and therefore costly — than it would if temperatures only rise 1.5 degrees.

That exponential difference means that different global strategies for addressing climate change also change the social and mortality costs of carbon. 

While Bressler’s model estimates that the social cost of carbon was $258 under current emissions, that number falls to $158 in a scenario where the world aggressively moves to reach net zero emissions by 2050.

These numbers can be used by business as well as governments, particularly given the heightened interest in environmental, social and governance metrics, Bressler notes. About 23 percent of corporations use some sort of internal carbon metric to guide their actions, according to McKinsey. 

Bressler’s mortality cost of carbon metric gives them the ability to calculate the impacts of their actions in deaths, not just dollars.

“It means that a company like Walmart could say, if we reduced emissions by 1 million metric tons, that saves 226 lives over the next 80 years,” he said.