Oftentimes, when we talk about climate change, it seems like something abstract and hard to quantify, and in some ways, it is. But climate change, in addition to all the damage it will cause, will kill people — a lot of them, according to a new study.

Study author R. Daniel Bressler, a PhD candidate at Columbia University’s Earth Institute and the university’s School of Public and International Affairs looked at how we calculate the cost of carbon and saw a gap. There wasn’t a clear way of translating the extra carbon in the atmosphere to human lives. He moved to address that.

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

Some estimates do exist. However, according to Bressler, they tend to rely on outdated research and don’t include sufficient ramifications.

For economists and policymakers, having access to such a number would be very useful, particularly in the context of a carbon tax — something which is discussed more and more as a way to tackle the ongoing climate crisis. Of course, the social cost of carbon is a highly complex number, it varies from country to country, and can be improved upon.

Bressler calculated that for every metric ton of carbon dioxide emitted beyond the current rate, there will be .000226. That doesn’t seem like a lot until you consider just how much carbon the world emits.

Look at it this way. For every 4,434 metric tons of CO2 we add beyond the current rate of emission, we kill one person — and 4,434 metric tons of CO2 is not really that much, either: that’s how much 3.5 Americans emit in their lifetime.

Still a wild underestimation

Bressler himself doesn’t claim his number is definitive and mentions that his estimate only considers direct temperature-related mortality, such as heat stroke. This leaves out possible deaths from storms, floods, crop failures, infectious diseases, or wars — all of which are very likely to accompany climate change, but much harder to quantify

So it’s quite likely that Bressel’s number is still a major underestimation.

The study also notes that if we stay on the current path, average temperatures will increase slowly to 2.1 degrees Celsius above pre-industrial times, after which the situation degenerates quickly, with temperatures reaching 4.1 degrees higher by 2100. Bressler estimates that if this turns out to be the case, we’d end up with 83 million excess deaths by 2100.

So what does this mean for a carbon tax?

The accurate price of carbon has been one of the main challenges in this type of discussion. Nobel-winning laureate William Nordhaus introduced the concept of a social cost of carbon. Nordhaus’s commonly used model, which Bressler builds on, proposes a cost of $37 per metric ton of carbon. But if we add the mortality cost of carbon, that price skyrockets to $258

There’s also another way of looking at this: it’s an opportunity to save millions or maybe tens of millions of lives. By cutting carbon pollution quickly, we could save around 74 million lives by the end of the century, the study concluded.

Ultimately, though, scientists can do their best, but it’s up to politicians to implement such policies — and politicians vary wildly in their opinions on climate (although climate and its very tangible effects are not themselves subject to opinion). In 2009, the Obama administration first mandated that scientists calculate the U.S. cost of carbon, and the figure at which government scientists arrived at was $51. Trump stopped almost all work on that front (and on climate science in general), later coming out with figures as low as $1 per ton. Now, an interim report from the Biden administration puts the price back at $52.

But even without these political biases, the odds of passing a real carbon tax are very slim at the moment. Whether or not adding people’s lives into the equation will make a difference remains to be seen.