Geography PhD student Christopher Callahan GR ’23 co-authored a study which received news attention after a recent report by the United Nations’ Intergovernmental Panel on Climate Change. In the study, Callahan described the impacts of extreme heat on economic productivity, which cost the global economy an estimated tens of trillions of dollars. Callahan sat down with The Dartmouth to discuss the findings of his research.
Climate change rarely seems to be discussed in economic terms. Why do you think that is?
CC: I think in some cases it’s because the economic impacts are not immediately obvious. There are major economic effects from, for example, extreme weather. We know that heat waves tend to kill crops and can damage infrastructure, and these are really visible effects for people. Certainly from the perspective of the agricultural sector, for farmers who grow crops, they are very aware of these socioeconomic impacts. But in a lot of other cases, researchers have found that climate change can put the brakes on economic growth in a more subtle way, in ways that are not immediately tied to a super obvious event like a hurricane. Nonetheless, they have longer term economic consequences.
What were the major findings of the study that you and Geography professor Justin Mankin published?
CC: We found that the emissions from major emitters, such as the United States and China, have substantially altered the economic output of many low-income countries worldwide. Our work attempted to understand the economic effects of climate change, but also specifically link those economic effects back to individual major emitters contributing to the devastation wrought by climate change.
Your research indicates that the effects of extreme heat related to climate change have cost the global economy tens of trillions of dollars in recent decades. How did these estimates become so substantial?
CC: The first reason is because we are looking at the issue globally. This is a number that is aggregated across as much of the globe as we can find, meaning that even in any one location, you may not be experiencing trillions of dollars in economic losses. But the numbers get to be pretty substantial once you add up the costs over the last 25 years. The second is illustrating the fact that extreme heat is one of the most substantial impacts of climate change. In many respects, it is one of the most direct ways that global warming will impact people. The costs of climate change may not be as easy to tally up in other cases, but in the specific case of extreme heat, those costs end up being quite large.
Can you describe the link between extreme heat and dire economic impacts?
CC: We know that heat waves can damage people, infrastructure and ecological systems. People get sick when it’s hot outside, and people can die when it’s hot outside. We know that infrastructure can melt or buckle or be damaged during short-term extreme heat events, and we know that crops are frequently destroyed. It also has a number of more subtle effects which are less thoroughly discussed. People are more likely to fall off ladders at work during heat waves, which imposes a productivity cost and a health cost. It’s all of these things that accumulate into these major economic costs.
The study you co-authored with professor Mankin describes the effects of climate change as “globally unequal.” How does the disparity between developed and developing nations manifest itself?
CC: It manifests itself in a couple different ways. This disparity tends to have its major effects in places that are already hot. Say you’re in a tropical region, such as South America, or Central Africa or Southeast Asia. Those regions are already close to the danger zone of extreme heat, so to speak. You’re already close to the physiological thresholds for people or crops where even a little bit more heat would be really damaging. Critically, though, more temperate regions are also the places that have contributed most to climate change via emissions. The result is a situation where the places that are most contributing to climate change are not feeling the brunt of its effects, while the places being most damaged by climate-driven extreme heat have barely contributed to the climate crisis.
How do you hope your scholarship informs the broader debate around climate change?
CC: One is focusing now and in the future on the ways in which climate change is already an economic problem. Global warming is not just a problem for our children but is a problem for us as well. I also do think that the ability to put things in economic terms is useful for people. It allows them to put a price tag on the cost we’re inducing and allows people to see that the costs of reducing our emissions are miniscule in comparison to the costs of those emissions in the first place. I do want to emphasize that economic costs are one of many effects of climate change. People are going to get sick. Cultural heritage sites are going to be damaged by rising seas. Species are going to be lost. All of these things can’t be captured in a price tag. We need to remain humble about our ability to tally up all the costs of climate change.
This interview has been edited and condensed for clarity and length.
