The explosion of home runs in Major League Baseball can be traced, in small part, to climate change, according to a study published Friday.
In a peer-reviewed paper published in the Bulletin of the American Meteorological Society, Dartmouth College researchers said they can connect at least 500 additional home runs from 2010 to 2019 to Earth's human-made warming.
The research was based on their simple premise that "air density is inversely proportional to temperature," according to the paper, and that with all "else being equal, warmer air is less dense and a batted ball will carry farther."
"In some ways this wasn't all that surprising," said Dartmouth doctoral student Christopher Callahan, who authored the paper with Nathaniel Dominy, a professor of anthropology; Jeremy DeSilva, the chair of the anthropology department; and Justin Mankin, an assistant professor who studies climate variability and the risks posed by global warming. “It was relatively straightforward. In some ways it was confirming that basic physical understanding that we already had."
From 1998, the first season of the 30-team MLB, through last year —and not including Covid-shortened 2020 — the number of home runs has varied annually from 4,186 in 2014 to 6,776 in 2019.
If current climate trends continue, researchers said, there will be 192 additional long balls per year by 2050 and 467 more per season by 2100, researchers said.
Home runs have been surging in MLB for decades with big league analytics operations pushing batters to swing for the fences as the most efficient manner to score, as opposed to more old-fashioned small-ball methods, such as hitting singles or stealing bases.
And Callahan was quick to point out that his team's research accounts for only a small part of the homer-happy trend.
"Certainly the analytics revolution has played a major role," Callahan said.
"We say that climate change has caused about 500 more home runs over the past 10 years [2010-19] but that's only about 1 percent of home runs. There's 5,000 a year, so we're only saying 50 per year. Those other factors are definitely more responsible as of now than global warming," he added.
From the start of pro baseball in the late 19th century through 1993, there was only one season when the average team hit more than 1 home run per game.
But starting in 1994, the average has topped 1 in all but four seasons. The top four homer seasons have all been recorded since 2017 — 1.39 in 2019, 1.28 in 2020, 1.26 in 2017 and 1.22 in 2021.
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In baseball lore, the 1927 New York Yankees are often regarded as the game's greatest team, boasting all-time greats Babe Ruth and Lou Gehrig. The 110-win "Murderers Row" team hit 158 homers in 155 games, an awe-inspiring total for the day but below average by 21st century standards.
So far in this very young 2023 season, there have been 1.19 long balls per game.
Perhaps not coincidentally, the average high temperature in the U.S. has also been steadily ticking up.
Homer hotbeds of the future will be in outdoor stadiums with more day games, as opposed to parks that are domed — and thus temperature-controlled — and host more night games, according to the Dartmouth research.
The ballparks that will have more climate-affected home runs will be Chicago’s Wrigley Field, Detroit’s Comerica Park, Minnesota’s Target Field and Denver’s Coors Field, researchers said.
And on the other end of the spectrum, venues that won’t feel the heat of climate homers will be St. Petersburg’s Tropicana Field, Miami’s LoanDepot Park, Houston’s Minute Maid Park and Phoenix’s Chase Field, which are all indoor facilities.
“One thing that I was surprised by was the amount of variations going forward. Places like Wrigley Field will see a lot more home runs in the future, because it’s open air and a lot of games are played in the daytime,” said Callahan, a Chicago native who grew up blocks away from Wrigley.
“And so you get a ton of more [climate-affected] home runs there, but you’ll get a lot fewer in places where there are domes and the games are more frequently played in the evening to start with. So you can get a lot of variation in different parks over time, and that’s something that surprised me.”
Gerald Meehl, a senior scientist at the National Center for Atmospheric Research in Boulder, Colorado, said he, too, sees connections the Dartmouth study made between climate and home runs.
“It’s an interesting application of climate change attribution and gets at a very baseball concept of shifting the odds towards a better chance of hitting home runs,” Meehl said.
Speaking as an avid baseball fan and less as a scientist, Callahan said he’s mostly afraid of global warming’s impact on humankind — but also mildly miffed about its influence on America’s pastime.
“I am a little bit disinterested in a game of baseball that’s all about home runs,” Callahan said. “I do like a little more action on the field. If it is the case that global warming will provide an extra incentive to just focus on home runs, I personally would not be super happy about that.”