Baseball hitters are getting more home runs, thanks to climate change.

Science reports on some unexpected consequences of a slightly warmer planet. In the statistics-heavy game of baseball, hitters have been averaging more home runs than ever for a lot of reasons – but one of them is warmer air creating less friction on the ball:

Because warmer air is less dense and exerts less drag on a batted ball, the number of home runs should in theory climb as global temperatures increase. And, sure enough, a new study shows that about 0.8% of the homers hit in Major League Baseball (MLB) since 2010 made it over the fence thanks to the extra distance global warming lent their flight.

During a game between the St. Louis Cardinals and the Milwaukee Brewers in 2012, former big-league catcher and broadcast commentator Tim McCarver wondered aloud whether climate change was driving an upward trend in home run rates across the sport. At the time, many fans and some scientists were dismissive. However, the idea resonated with Christopher Callahan, a climate scientist and baseball fan at Dartmouth College.

To find out whether rising temperatures and decreasing air density played a role in home run rates, Callahan and his colleagues delved into the copious data MLB keeps. In addition to keeping home run stats for decades, since 2015 MLB has used an automated system of cameras and computers called Statcast to track the velocity and trajectory of every ball thrown or hit in every game. “MLB is obsessed with collecting data on itself, so we have this treasure trove of numbers,” Callahan says.

The researchers tracked game-day temperatures and homers from 100,000 MLB games between 1962 and 2019 at stadiums at various elevations across the country. To control for the launch angle and speed of each batted ball–and thus the skill of both pitchers and batters in varying temperature conditions –they combed through high-speed Statcast camera footage of 220,000 individual hits between 2015 and 2019. Both analyses returned the same effect: On average, a 1°C increase in air temperature on game day correlates with nearly a 2% uptick in the number of home runs per game. Each additional degree of global warming results in an additional 95 home runs per baseball season, and more than 500 home runs since 2010 can be attributed to anthropogenic warming, the researchers report today in the Bulletin of the American Meteorological Society. “I think we’ve vindicated McCarver,” Callahan says.

However, those extra homers represent a tiny fraction of the more than 65,300 hit since 2010. They also account for only a drop in the tsunami of home runs that has inundated MLB. Over the past 4 decades, home runs have increased by 34% per game.