Home runs in baseball have been getting steadily more common for decades, and a recent spike in home runs might be driven by anthropogenic climate change. A new analysis combined decades of baseball statistics and ballistics data with predictive climate modeling. The study showed that more than 500 home runs since 2010 can be attributed to climate-driven, unseasonably hot temperatures. If climate change keeps warming the globe, some teams will continue to see more home runs while others will remain largely unaffected.
“I’m a baseball fan and I’m a climate scientist, too,” said lead researcher Christopher Callahan, a doctoral student in geography at Dartmouth College in Hanover, N.H.
The idea for this research came from an established physics concept: When it’s hotter outside, the air gets a little bit thinner. This is hardly noticeable in most cases, unless you’re a 100-mile-per-hour baseball rocketing toward the outfield.
“I was curious about whether you could see this in the large-scale data, and it turns out that you can,” Callahan said.
Going, Going, Gone!
Callahan and his colleagues analyzed temperature trends and home runs from more than 100,000 Major League Baseball (MLB) games from 1962 to 2019. They also included advanced ballistics data on more than 220,000 batted balls from 2015 to 2019 using baseball’s high-speed Statcast camera system. Ballistics data allowed the researchers to account for the effects of playing in different stadiums and to compare batted balls of the same launch angle and speed. This helped them isolate the impact of temperature on the number of home runs.
“It’s a real signal of the way that climate change is having such a pervasive impact.”
The researchers then combined these baseball analytics with predictive climate models, allowing them to calculate the likelihood that anthropogenic climate change, rather than a random temperature anomaly, caused a day to be unseasonably hot.
The analysis showed that for every 1°C temperature increase, there was a roughly 2% increased chance per game that a fly ball would be a home run. A total of 577 homers from 2010 to 2019 can be attributed to human-caused warming—that’s an average of about 58 per year. Looking forward, the researchers predicted an increase of around 95 home runs per season for each 1°C increase in temperature.
“It’s a real signal of the way that climate change is having such a pervasive impact,” Callahan said, “and an impact on things that are not just hurricanes and heat waves, but more subtle changes in every part of our lives.”
Not every baseball field will see the same increase in home runs. “Wrigley Field will have the most increase in home runs in the future, because it mostly [plays] day games when the temperatures are hottest,” Callahan said. “Whereas in places that play mostly night games, the temperatures are a lot milder, so you will have less of an increase” in home runs.
On the other end of the spectrum, “Tropicana Field in Tampa Bay [Florida] is covered all the time. It’s the only nonretractable dome in baseball, and so it’s the one place where this is just not going to be a problem.”
The results were published in the Bulletin of the American Meteorological Society.
The Climate Changeup
Callahan explained that the analysis was possible because baseball is such a data-rich environment. “That’s great from our perspective—it’s a real treasure trove.” But the project also hints at the hidden effects of climate change that are undiscoverable because data are lacking, he added.
“It really illustrates that there are times when we end up looking for our keys under the lamppost because that’s where the light is.” Future work will explore how climate-driven heat also affects player performance.
Jim Albert, a statistician at Bowling Green State University in Ohio, noted that although these results are statistically significant, the number of home runs attributable to climate change is small relative to other ball and player effects.
“I don’t know that we’ve seen a baseball game canceled for heat yet, but I think it’s coming.”
Albert, who was not involved with the new analysis, contributed to MLB-commissioned reports that investigated the recent rise in home runs. The new results “are similar to our findings on the effect of temperature,” he said. “The novel aspect of this paper is the exploration of the effects of global warming on home run hitting.”
Callahan speculated that there will likely come a point when team owners decide that the increase in home runs isn’t worth the heat-related health risks to players and fans. “I don’t know that we’ve seen a baseball game canceled for heat yet, but I think it’s coming,” he said. Teams might opt to shift from day games to night games, invest in a domed stadium, or even relocate to a cooler city—mitigation strategies that could have profound economic impacts on a region.
“If the effects of global warning increase as the authors predict,” Albert said, “then I believe MLB should use this information in future plans about scheduling of games and the construction of the ball.”
—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer
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