Hotter weather could be changing baseball

'Climate ball' isn't necessarily a good thing.
Aaron Judge of the New York Yankees hits a home run against the Boston Red Sox during the eighth inning at Fenway Park on September 13, 2022 in Boston, Massachusetts.
Aaron Judge of the New York Yankees hits a home run against the Boston Red Sox during the eighth inning at Fenway Park on September 13, 2022 in Boston, Massachusetts. Maddie Meyer/Getty Images

As average global temperatures continue to rise, America’s pastime could be entering the “climate-ball era.” A report published April 7 in the Bulletin of the American Meteorological Society found that since 2010, more than 500 home runs can be attributed to higher-than-average temperatures. These higher-than-average temperatures are due to human-made global warming.

While the authors of this study only attribute one percent of recent home runs to climate change, their study found that warmer temperatures could account for 10 percent or more of home runs by 2100, if emissions and climate change continue on their current trajectory.

[Related: What’s really behind baseball’s recent home run surge.]

“Global warming is not just a phenomenon that shows up in hurricanes and heat waves—it’s going to alter every aspect of how we live and play,” study co-author and doctoral candidate in geography at Dartmouth University Chris Callahan tells PopSci in an email. “Reducing human emissions of greenhouse gasses is the only way to prevent these effects from accelerating.”

This study primarily arose because Callahan, a huge baseball fan, was interested in any possible connections between climate change and home runs. “This simple physical mechanism—higher temperatures mean reduced air density, which means less air resistance to batted balls—had been proposed previously, but no one had tested whether it shows up in the large-scale data. It turns out that it does!” Callahan says. 

Callanhan and his team analyzed more than 100,000 Major League Baseball (MLB) games and 220,000 individual hits to correlate the number of home runs with the occurrence of unseasonably warm temperatures during the game. Next, they estimated how much the reduced air density that results from high air temperature was a possible driving force in the number of home runs on one given day compared to other games. 

Other factors, such as performance-enhancing drugs, bat and ball construction, and technology like launch analytics intended to optimize a batter’s power were also taken into account. While the team does not believe that temperature is the dominant factor in the increase in home runs, particularly because present day batters are primed to hit the ball at optimal angles and speeds, temperature does play a factor.

Increase in average number of home runs per year for each American major league ballpark with every 2 degree Fahrenheit increase in global average temperature. CREDIT: Christopher Callahan

The team particularly looked at the average number of home runs annually compared to every 2 degrees Fahrenheit increase in local average temperature at every MLB ballpark in the US. They found that the open-air Wrigley Field in Chicago would experience the largest spike (more than 15 home runs per season per 2 degree change), while Tampa Bay’s dome roofed Tropicana Field would stay level at one home run or less regardless of how hot it is outside the stadium. 

[Related: Will baseball ever replace umpires with robots?]

Night games lessened temperature and air density’s potential influence on the distance the ball travels, and covered stadiums would nearly eliminate the influence. Additionally, the study did not name precipitation as a factor, after all, most games are postponed or delayed. The number of runs per season due to temperature could be higher or lower depending on the conditions on each game day.

“I think it was surprising that the [heat’s] effect itself, while intuitive, was so clearly detectable in observations. As a non baseball fan, I was astounded by the data,” study co-author and geographer Justin Mankin tells PopSci. Mankin also noted that some next steps for this kind of research could potentially be looking into how wooden bats should change due to warming and how other ballistics based sports (golf, cricket, etc.) are affected by the increased temperature. 

While more home runs arguably makes for more exciting games, exposure to players and fans to extreme heat is a major risk factor that MLB and its teams will need to consider more frequently as the planet warms. 

“A key question for the organization at large is what’s an acceptable level of heat exposure for everybody and what’s the acceptable cost for maximizing home runs,” Mankin said in a statement. “Home runs are one pathway by which temperature is affecting game play, but there are other pathways that are more concerning because they have human risk attached to them.”