The Increase in Baseball's Home Runs is Attributed to Climate Change

Baseball, the world's best sport for number enthusiasts, has been the subject of extensive data collection, with its analysis even having its own name: sabermetrics. While team managers, coaches, and players use these statistics for game strategy, the massive amount of available data can also be utilized for other purposes.

Researchers have delved into baseball's wealth of data and discovered that climate change has resulted in over 500 home runs since 2010, with higher air temperatures contributing to the sport's ongoing home run heyday. The findings were published in the Bulletin of the American Meteorological Society on April 7.

Many factors have contributed to players hitting more home runs in the last four decades, such as steroid use and the height of the ball's stitches. According to Christopher Callahan of Dartmouth College, "Blog posts and news stories have also speculated about whether climate change could be increasing the number of home runs. But nobody had quantitatively investigated it."

As a climate change researcher and baseball enthusiast, Callahan decided to investigate the question by delving into the sport's vast amount of data in his free time. Two researchers from different fields joined the project after Callahan gave a brief presentation on the topic at Dartmouth.

The resulting analysis is methodologically sound and “does what it says,” according to Madeleine Orr, a researcher on the impacts of climate change on sports at Loughborough University London, who was not involved in the study.

The relationship between global warming and home runs is rooted in fundamental physics: as temperature rises, air density decreases, reducing air resistance. Callahan and his colleagues took various approaches to determine whether home runs were occurring as a result of warming.

First, the team investigated the effect at the game level. Across more than 100,000 Major League Baseball (MLB) games, the researchers discovered that a 1-degree Celsius increase in the daily high temperature resulted in almost a 2% increase in the number of home runs in a game. For example, a game similar to the one that occurred on June 10, 2019, where the Arizona Diamondbacks and Philadelphia Phillies set the record for the most home runs in a game, would have had 14 home runs instead of 13 if the temperature had been 4 degrees Celsius higher.

The researchers then used a climate model to calculate game-day temperatures while controlling for greenhouse gas emissions and discovered that human-caused warming led to an average of 58 additional home runs per season from 2010 to 2019. The analysis also revealed that the trend of more home runs in higher temperatures dates back to the 1960s.

The team then analyzed over 220,000 individual batted balls using the Statcast system, which has tracked the trajectory and speed of every ball hit during a game since 2015. The researchers compared balls hit in almost the same way on days with different temperatures, controlling for variables such as wind speed and humidity. The analysis revealed a similar increase in home runs per degree Celsius as the game-level analysis, with only lower air density due to higher temperatures accounting for the increased number of home runs.

While climate change has "not been the dominant effect" contributing to more home runs, Callahan believes that "if we continue to emit greenhouse gases strongly, we could see much more rapid increases in home runs" moving forward.

According to Callahan, the abundance of home runs has made baseball duller for some fans, and it is partially why Major League Baseball has introduced several new rule changes for the 2023 season.

Teams can adjust to rising temperatures by shifting day games to night games and adding domes to stadiums, according to the researchers, who discovered no temperature-related effect on home runs for games played under a dome. However, Orr believes that even with those adaptations, climate change may cause more drastic changes to America's pastime in the future.

Because the sport is susceptible to variability in snow, storms, wildfires, flooding, and heat at various points during the season, Orr believes that "Without substantial change, baseball exists in the current model" within 30 years.

Callahan concurs, stating that "This sport, and all sports, are going to see major changes in ways that we cannot anticipate."

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