The Blue Jays’ home opener on Tuesday night at the newly renovated Rogers Centre was a crackerjack game. After the Detroit Tigers scored early with a three-run homer off starting pitcher Alek Manoah, the Jays roared back with five home runs – the most ever for a home opener – and a final score of 9 to 3.
Did they get a hand from climate change? A new report, Global Warming, Home Runs, and the Future of America’s Pastime, studied data from more than 100,000 Major League baseball games over the past 60 years and concluded that rising temperatures may have added more than 500 home runs to the league’s tally since 2010.
Further, while only one per cent of recent homers can be attributed to warmer temperatures, the study, led by Christopher Callahan, a doctoral candidate in geography at Dartmouth University in New Hampshire, found that by 2100 that figure could rise to 10 per cent based on climate-change forecasts.
The science behind the study is quite simple. “The ideal gas law tells us that air density is inversely proportional to temperature,” the report notes. “Ballistics tells us that the trajectory of a batted ball is influenced by temperature via its effect on density. All else being equal, warmer air is less dense, and a batted ball will carry farther.”
It adds: “The well-documented rise in home runs has coincided with a long-term increase in game-time temperatures at baseball stadiums, and a resulting decrease in air density during games. These trends have fueled spirited debate among commentators and sportswriters, including controversial arguments concerning the role of global warming, but a formal analysis linking human-caused climate change and home run totals has not been performed to date.”
Until now. The study, published in the Bulletin of the American Meteorological Society, found that an increase of 1 degree C in the daily high temperature on game day would increase the number of home runs by 1.96 per cent on average, with a greater increase (2.4 per cent) for games played in the heat of the early afternoon, and a smaller bump (1.7 per cent) for night games.
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The researchers also looked at more than 220,000 individually batted balls using Statcast data from 2015 to 2019, which let them note the precise angle and speed of every ball that was hit. This method also found a small but measurable increase in home runs from identically hit balls on warmer days, meaning the higher temperature allowed the ball to travel further — and potentially out of the park.
We’re used to seeing climate-change goals couched in terms of sea-level rise or habitat loss. Callahan’s study notes that “limiting global warming to 1.5 C instead of 2 C would avoid an additional 1,865 home runs” by 2100. Limiting warming to 2 C instead of 3 C would avoid an additional 3,891. It also says that converting all day games into night games would mitigate the change, but adds that’s unlikely.
There is one additional data point worth mentioning. “The effects described above include all games played in open-air stadiums and in retractable-roof stadiums when the roof is open,” the report says. “In the remaining … games, which are played under closed domes, we find only small and insignificant effects of temperature, as covered games are less exposed to ambient weather.”
Toronto had an unseasonably warm daytime high of 24 C on Tuesday, but the roof of the Rogers Centre remained closed. In other words, the Jays’ home-run derby was all their own doing.