Baseball is a renowned warm-weather sport. Now scientists have identified one way high temps can reward batters: It can help convert a strong hit into a home run.
The sport has seen a recent home-run heyday, and climate change appears to have played some role.
Scientists are now linking warming air temps to more than 500 extra home runs since 2010. Christopher Callahan of Dartmouth College in Hanover, N.H., and his colleagues reported their findings April 7. It appears in the Bulletin of the American Meteorological Society.
The finding comes from mining mountains of statistics on the game. In fact, baseball is the best sport in the world for numberphiles. There are so many stats collected that the analysis of them even has its own name: sabermetrics. As the 2011 movie Moneyball showed, team managers, coaches and players use these statistics in hirings, lineups and play strategy. But the mountain of available data can be put to other uses, too.
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From steroid use to the height of the stitches on a ball, many factors have had some role in how often players have been able to hit a ball out of the park over the last 40 years. But in recent years, blog posts and news stories have speculated about whether climate change might be upping the number of home runs, says Callahan. He’s a PhD student in climate modeling and impacts. Until now, he notes, nobody had investigated it by looking at the numbers.
So in his free time, this scientist and baseball fan decided to dig into the sport’s mounds of data. After he gave a brief presentation at Dartmouth on the topic, two researchers in different fields decided to join him.
The method they used is sound and “does what it says,” says Madeleine Orr, who was not involved with the study. In England, she studies the impacts of climate change on sports. She works at Loughborough University London.
How they identified climate’s impact
The idea that global warming might affect home runs stems from fundamental physics: The ideal gas law says that as temperatures rise, the air’s density will fall. And that will cut air’s resistance — friction — on the ball.
To look for evidence of such a climate link to home runs, Callahan’s team took several approaches.
First, they looked for an effect at the game level.
Across more than 100,000 major-league games, the researchers found that for every rise of 1 degree Celsius (1.8 degrees Fahrenheit) in a day’s high temperature, the number of home runs in a game rose by nearly 2 percent. Take, for example, a game on June 10, 2019, when the Arizona Diamondbacks played the Philadelphia Phillies. This game set the record for most home runs. The game would be expected to have had perhaps 14 home runs — not 13 — if it had been 4 degrees C warmer that day.
The researchers ran game-day temperatures through a computer model for climate. It accounted for greenhouse gas emissions. And it found that warming linked to human activities led to an average of 58 more home runs each season from 2010 to 2019. In fact, it showed an overall trend of more home runs on warmer days going as far back as the 1960s.
The team followed up on that analysis with a look at more than 220,000 individual batted balls. High-speed cameras have tracked the trajectory and speed of every ball hit during a major league game since 2015. These data are now available through what’s known as Statcast.
The researchers compared balls hit in almost exactly the same way but on days with different temperatures. They also accounted for other factors, such as wind speed and humidity. This analysis showed a similar increase in home runs per each degree Celsius rise. Only lower air density (due to higher temperatures) appeared linked with an excess in home runs.
To date, climate change has “not been the dominant effect” causing more home runs, Callahan says. However, he adds, “If we continue to emit greenhouse gases strongly, we could see much more rapid increases in home runs” moving forward.
Baseball’s future could be quite different still
Some fans feel that a growing bounty of home runs has made baseball less fun to watch. This is at least part of the reason that Major League Baseball unveiled several new rule changes for the 2023 season, Callahan says.
There are ways teams can adapt to rising temperatures. Many could shift day games to night games, when temps tend to be cooler. Or they could add domes to stadiums. Why? Callahan’s group found no effect of outdoor temperature on home runs in games played under a dome.
But climate change may soon prompt even more dramatic changes to America’s pastime, Orr says. Keep in mind, this sport is susceptible to snow, storms, wildfires, flooding and heat. In 30 years, she worries, “I don’t think, without substantial change, baseball exists in the current model.”
Callahan agrees. “This sport, and all sports, are going to see major changes in ways that we cannot anticipate.”