How Will Rising Temperatures Change Baseball?

Angrier players and more home runs are on the way if summer heat keeps breaking records.

Washington Nationals shortstop Ian Desmond drapes a towel over his head to cool off in 100-degree heat.
Washington Nationals shortstop Ian Desmond cools off in 100-degree heat. (Tami Chappell / Reuters)

Can hot weather affect how often pitchers hit batters with baseballs? In 2011, Rick Larrick, a management professor at Duke University’s Fuqua School of Business, came up with an answer. By analyzing decades of game-day data, he and three colleagues determined that each baseball season logs approximately 190,000 at-bats, and roughly 1,550 hit batters. The odds of retaliation after a batter has been plunked—that is, a pitcher hitting a batter to even the score—were 27 percent when air temperatures were in the 90s, but only 22 percent when they were in the 50s.

Yes, the researchers adjusted for variables like wild pitches and hanging curveballs.

“If none of your teammates have hit earlier in the game, there’s really no relationship [between temperature and] a pitcher hitting a batter,” says Larrick. “But as soon as you’ve had one or more of your teammates hit earlier in the game, it’s increasingly likely to have a pitcher hit a batter on the other team [as temperatures rise].”

Hot weather’s ability to stir up aggressive behavior has been well documented. According to a 2013 study published in the journal Science, “climate’s influence on modern conflict is both substantial and highly statistically significant.” Baseball, it seems, is no exception. As Larrick points out, “When we’re in an agitated state, we’re more ready to see hostility and want to retaliate.”

Considering that this past summer was the hottest on record, and that scientists predict temperatures will continue to rise about 3.6 degrees Fahrenheit over the next half-century, it stands to reason that more changes are in store for the planet—and the game of baseball.

For example, if pitchers’ moods change in the heat, what about the mood of the ball? How does a baseball react—how does it travel—in hot weather? Michael Mann, a climate scientist and director of Penn State’s Earth System Science Center, writes via email that the ball reacts differently in the heat, and the reason is the density of the air. Hot, humid days are less dense than cool, dry ones.

“If we change the density of the atmosphere near the surface of the earth, that will influence the behavior of objects that are thrown or hit through the atmosphere,” he writes. “That of course includes baseballs. Lower density means less air resistance, which would mean balls would get hit farther.”

In other words, all conditions being equal, a long fly ball that reaches the warning track in April might be a home run on a scorching day in July.

Which brings us to Arlington, a neighbor of Dallas, and home of the Texas Rangers. There, temperatures routinely reach the 90s throughout the summer. This past August alone, the thermometer topped 100 on 12 different days.

Former Rangers head trainer Danny Wheat spent two decades conditioning the Rangers to play in Arlington Stadium, then Globe Life Park, neither of which had a roof. “It seemed like, from June to September, we started every game at seven o’clock, and it was 97, or 100-plus,” he says. “And the sun didn’t go down until nine or nine-thirty. You’re into the sixth inning by then. Even at the end of the game, it would be 90 degrees.”

To combat dehydration, Wheat pumped his players with electrolytes in the form of Gatorade, Powerade, and Pedialyte. Nonetheless, by August and September, his players were noticeably weaker than they were in April and May. “We always had what seemed to be a lot more soft-tissue leg injuries than some of the other clubs. Hamstrings, calf injuries, from guys running the bases,” he says. “Our staff attributed that to the excessive heat and the fatigue.”

But the extreme heat came with a bonus: fly balls carried. “It was common knowledge that the ball travels better in the heat, and it’ll travel better in the summer than in April or May,” Wheat says. “Oakland’s a perfect example of that. It’s cool and dry there at night, and it’s very hard to hit a home run. That was a place where everybody said they liked playing day games because that was the only chance they had to hit a homer.”

Wheat’s anecdotal evidence is backed by physicist Alan Nathan, whose current research is on baseball—specifically, the collision of the bat with the ball and the aerodynamics of a baseball in flight. Nathan, a professor emeritus of physics at the University of Illinois, says, “You’ll see the ball, on average, travel a little bit farther in Texas than in other venues. Pitchers don’t want to play there, batters do. It’s a hitting environment.”

According to Nathan, however, “Far and away the biggest effect on air density is altitude.” Fly balls, he explains, carry 20 to 30 feet farther in Coors Field, the home of the Denver-based Colorado Rockies, where games are played nearly a mile above sea level. That’s one reason why the Rockies store their baseballs in a humidor: doing so levels the playing field. A damper, heavier ball flies off the bat less forcefully than a dry one, and, therefore, travels a shorter distance.

Low air density—be it from high altitude or the planet’s rising temperatures—also affects balls when they’re pitched, especially breaking balls that rely on air resistance to curve, drop, or slide. Pitchers may not realize it, but the lower the air density, the less their pitches will move. “The typical air density in Denver is about 80 percent of sea level,” Nathan says. “So there’s 20 percent less movement on a curve ball. Fastballs appear to be a little faster, though, because there’s less air resistance.”

What about the knuckleball—that butterfly of a pitch that doesn’t spin, but floats? A knuckleball, Nathan points out, relies even more on air density. A knuckler will bounce more in denser air—so practitioners like Boston’s Steven Wright would be wise to avoid high altitudes, such as the one found in Coors Field. Where should Wright pitch? According to Nathan, anywhere closer to sea level.

So if predictions turn out as expected, and temperatures do rise nearly four degrees Fahrenheit in the next 50 years—what kinds of changes might we notice on the baseball field?

“Over the course of a given season, there are something like 4,500 home runs in major league baseball,” he says. “And for every home run, there are a lot of near misses. As the temperature climbs, those near misses will start flying over the wall.”

That leaves the Texas Rangers with a conundrum. They’re about to spend $1 billion to build an air-conditioned, retractable-roof stadium. The cooler, denser air will most likely help their pitchers—breaking balls will break, knucklers will knuckle, and sliders will slide. But their hitters might want their old ballpark back.