By Cate Twining-Ward

Cate Twining-Ward recently interviewed Columbia University PhD candidate R. Daniel Bressler to discuss his work in developing economic models to predict the impacts of climate change—most notably, his groundbreaking article “The Mortality Cost of Carbon.” 

In July 2021, Columbia University PhD candidate R. Daniel Bressler, better known as Danny by his peers, published an article in Nature Communications entitled “The Mortality Cost of Carbon." As the title suggests, the study predicts the mortality cost of carbon: the number of human deaths caused by carbon dioxide. To many, his results are haunting: adding 4,434 tonnes of carbon dioxide, equivalent to the average lifetime emissions of 3.5 Americans today, raises global temperatures enough to cause at least one temperature-related death between 2020 to 2100.  

Bressler’s paper builds on work by William Nordhaus, who received the 2018 Nobel Prize for Economics for developing the “social cost of carbon.”

The social cost of carbon is a number, expressed as a dollar value. This number tells us what the future damages of carbon dioxide emissions are expected to cost. In 2021, the United States estimated that every additional metric ton of carbon dioxide emitted lead to $51 worth of damages.

Mr. Bressler argues that this model is limited, as it does not account for the number of premature deaths that climate change is expected to cause. Bressler extended Nordhaus’ model to account for premature deaths, and found that after doing so, the social cost of carbon is far, far higher: $258 per metric ton.

Three years after publishing his seminal paper, Mr. Bressler, 33, is in his final year of completing a PhD in Sustainable Development. Now, he is engrossed in an even larger academic undertaking. His new work attempts to break down exactly where deaths caused by carbon dioxide will occur, on a country-by-country basis.

I sat down with Mr. Bressler in Columbia’s Philosophy Hall, where we spoke for several hours over the noisy acoustics of a university espresso bar. Here, Bressler can be found most weekdays, immersed in his work at a makeshift standing desk alcove, framed by two monitors, his laptop, and a tablet for sketching models, algorithms, and graphs. Below is a condensed version of our conversation.

How did you first become interested in climate change economics?

As a kid I’d often get to visit the Field Museum in Chicago. They showed the natural history of the world all the way from 4.6 billion years ago to the present and all the mass extinctions in between. I remember being so young and just having this intense realization that humans are only this tiny little thing at the very end of a long-time scale, and then before you know it, you’re in the gift shop.

I was consumed by this idea that the world is constantly changing, and then also troubled by the rapid rate of change. And so, I became interested in various environmental problems, including climate change.

How did the reaction towards your paper The Mortality Cost of Carbon change the trajectory of your PhD?

Well, lots of people reached out to me and lots of people are now using it. I think the feedback was pretty overwhelmingly positive.

How does your model demonstrate the tangible impacts of carbon dioxide?

My model projects the total number of deaths caused by climate change. It also calculates the mortality cost of carbon. This is the number of projected deaths caused by every additional ton of carbon dioxide emitted.

In principle, climate-mortality can, and does, result from many factors—extreme storms, flooding, infectious disease, food insecurity, conflict, and so forth. But in practice, I did not find studies on pathways other than temperature-related mortality that met the criteria that I specified in the paper. So, my paper only accounts for temperature-related morality, which is the net impact of there being more hot days and fewer cold days.

Now that you have determined a global average of projected deaths due to carbon dioxide, do you plan to explore how CO2 emissions disproportionately impact people living in different parts of the world?

That’s exactly what I am working on now. The mortality cost of carbon paper said, “Hey, there are these deaths that are occurring around the world due to carbon dioxide emissions.” But naturally, there's a question of where those deaths are occurring.

And what have you found?

What I'm finding so far is that it's heavily, heavily concentrated in the Global South—in hotter and poorer countries. In separate work, I am also trying to look at the age-specific impacts to understand more about who is dying, instead of just aggregating everyone together, as the first paper did.

The first paper was a step in the right direction but now it’s about understanding the distribution of the impacts, and who is being impacted. And because the impacts are distributed so unequally, choices around valuing lives and livelihoods become extremely important. For instance, the decision on whether to use income weighting—which was just recently sanctioned for use by the US government—is important.

Can you explain how the government uses income weighting? 

Income weighting essentially counts everyone’s welfare equally as opposed to counting everyone’s dollars equally. When you just count everyone’s dollar equally you end up valuing the lives of rich people more than the lives of poor people. Now the US government can account for this when conducting a benefit-cost analysis of major regulations. In recent work, we’re finding that the social cost of carbon changes a lot when income weighting.

What is your hope for your new paper in terms of impacting climate policy?

I view it much more so as trying to pull back the onion and be more straightforward about what these economic models are doing. So, showing people that, hey, yes, we're getting a final number that represents the damage from a tonne of carbon dioxide emissions and that is this monetized number. But to me, it’s not just about producing a monetized number. It’s also then saying, “Hey, there are these intermediate outputs along the way that are very important that you should know about.” I think you make better policy choices when you thoroughly understand the underlying models and outputs that you're using.

So, you're not trying to push a certain policy. You’re just saying this is the research, this is what is happening, and then the public and the policymakers can use that information to make informed decisions.

Yeah, exactly. It's my job to do the research, try to get the best understanding of what the underlying truth is, and to make it accessible to people. I think it is an issue if there are a lot of complicated things under the hood that are going on, some of which are normative choices and some of which are physical projections, that all get mixed together in a final number.

Some experts might be aware of these choices, but most users of the model’s outputs probably are not. And even the experts may not be able to disentangle these intermediate outputs.

I think it's important for transparency in any science to show the steps along the way to your final number. Just producing some final number… that is not a good approach.  

There are a lot of implicit moral and philosophical questions embedded in economic models. How do you navigate that?

I think it's really important that economists are clear about the choices that are made around valuing lives and livelihoods. These choices are not just some physical laws of nature that no one can question.

The social cost of carbon is a function of physical projections and of decisions made around valuing lives and livelihoods. And there’s a lot of contentious assumptions made to get to that number.

These are heavy topics. How do you unwind?

I do competitive stair climbing. You race about in skyscrapers. I actually have a big event coming up in April!

Cate Twining-Ward (MPA ‘24) is a reporter for The Morningside Post. At SIPA, she studies Environmental Science and Policy. Prior to SIPA, she worked at the United Nations on Sustainable Development, with NGOs to scale environmental education programs in west and east Africa, and as a senior correspondent for Planet Forward, an environmental journalism organization. Her work at Columbia has focused on addressing the climate crisis through the research and implementation of environmental justice policy, sustainable food systems, and system change.