It started with an avid baseball fan pondering how rising temperatures could affect America’s favorite pastime. But, with his doctoral student cap on, Christopher Callahan saw the question as an opportunity.

Intellectual curiosity like that drives so much of what we do at Dartmouth. This particular inquiry inspired an interdisciplinary collaboration that illustrated how looking at climate change through the lens of baseball can impact social change.

Field. Study.

Home runs have been steadily on the rise since the 1980s. This upward trend could be explained in a variety of ways, and one speculation was a reduction in ballpark air density. This theory was at the heart of Callahan’s study.

Callahan, a doctoral candidate in geography, assembled a research team, all with ties to the Ecology, Evolution, Environment & Society graduate program: Nathaniel Dominy (professor of anthropology), Jeremy DeSilva (professor of anthropology and department chair) and Justin Mankin (assistant professor of geography).

Together, the team explored whether there are more home runs on unseasonably warm days than on unseasonably cold days during the course of a season. Their research took them from deep data archives to ballparks across the nation. The resulting paper, “Global Warming, Home Runs, and the Future of America’s Pastime,” was published by the Bulletin of the American Meteorological Society in May 2023.

Discoveries on the Diamond: Running the Numbers

To correlate the number of home runs with the unseasonably warm weather, the team analyzed more than 100,000 major league games and 220,000 individual hits. Their research accounted for factors such as the construction of bats and balls, the use of performance-enhancing drugs, and the advancements in technology that help optimize a batter’s power and distance.

Callahan and company found a clear physical mechanism at play in which warmer temperatures reduce the density of air, but it’s not the dominant factor behind increasing home runs. This research, however, identifies its effect—and it could become more significant over time. To gauge how the average number of home runs per year could rise along with a rising average temperature, they examined each major league park in the United States. Among the data: Wrigley Field in Chicago would see the largest spike in home runs at 15 per season, whereas Tropicana Field in Tampa would remain level, no matter how hot it gets.

But there’s a bigger picture here, Mankin explains: “Home runs are one pathway by which temperature is affecting gameplay; there are others that are more concerning because they have human risk tied to them.”

American Pastime. Global Future.

Callahan was drawn to this research because climate change can and will alter our lives and the things we care about in subtle ways; it’s not just the threat of megadroughts or category 6 hurricanes. Studies like this, the researchers believe, serve as an entry point for understanding a phenomenon that affects the planet and every living thing on it, especially for people who wouldn’t otherwise give it serious thought.

“Maybe people will have a bigger conversation about the more impactful and dangerous aspects of climate change once they know how it’s affecting this quintessential game,” says DeSilva. After all, baseball has been a touch point of social change in the past.

Dominy explains how opposing cultural values are expressed in baseball: winning and losing, tradition and change, teamwork and individualism, logic and luck. Those same tensions, he says, are frustrating our collective response to carbon emissions.

“So it’s extremely fitting to explore the effects of climate change on baseball. It is a potent metaphor for the American experience.”

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The research happening at Dartmouth today builds off a rich history of life-altering, game-changing innovation, which includes the first-ever clinical X-ray in 1896 and the birth of the BASIC computer programming language—and it also fuels the future of discovery across our institution.