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Home Runs Are One Way Climate Change Affects Baseball. Here Are 11 More.

It’s getting hot in here, so close up all your domes

A baseball player swinging a thermometer.
Heatmap Illustration/Getty Images

Home runs ain’t the half of it.

Last week, the Bulletin of the American Meteorological Society issued a widely cited report that found global warming is “juicing” baseballs. The result is an extra 50 or so home runs per year in the major leagues. “It’s basic physics,” The Associated Press explained. “When air heats up, molecules move faster and away from each other, making the air less dense. Baseballs launched off a bat go farther through thinner air because there’s less resistance to slow the ball.”

Baseball fans have long been aware that hot weather makes for more home runs, so it follows that increasing temperatures will have an impact on the game in the years ahead. But MLB has more to worry about than the game becoming boring again because of too many dingers. Here are a few more ways climate change could irrevocably alter the future of America’s favorite past time:

1. Fastballs will get faster and curveballs less curvy.

We’ve already covered how the ball will behave differently off the bat. But what about out of the hand?

Heat and high humidity mean less air density, which in turn causes “fastballs to be faster, curveballs to curve less, and spin rates of pitches to be higher,” wrote Lawrence Rocks for SABR’s “Future of Baseball” issue in 2021. Of course, “these factors will cause pitchers to change their usage percentages on their pitch selection.”

As lowland parks grow hotter, we can expect them to behave more like the famously thin-aired Coors Field in Denver — particularly Atlanta, Kansas City, and Houston, which have among the lowest air densities of the Major League stadiums. Heat and humidity will cause baseballs to move more quickly out of the hand while the reduction in the Magnus force will cause them to break more poorly. And if fastballs get faster and curveballs break less, you can naturally expect to see more heaters in the game — and potentially more strikeouts as a result.

2. Games will be “smoked out.”

At the time of first pitch in Seattle, the Air Quality Index was 220. During the nine innings that followed, it would peak at 240 — more than twice the satisfactory level and “unhealthy for all groups.”

The year was 2020, and wildfires up and down the West Coast were making the empty stadiums even more apocalyptic. Shortly after smoke turned the Bay Area a dystopian orange, MLB decided to move home games from Seattle to San Francisco’s Oracle Park — because the air quality in the Pacific Northwest at that point was too unsafe for athletes.

It won’t be the last time baseball games are moved or even postponed due to air quality from fires. In 2022, perhaps against better judgment, the Mariners played the ALDS against the Astros when the AQI was 158. Though the unwritten rule is to postpone games when the AQI tops 200, players are beginning to push back, saying — rightfully — that prolonged exposure to inhaling smoke is dangerous. “It’s not like if you’re below 200, everything is fine, and if you’re above 200, everybody is severely affected,” a public health official pointed out to The Athletic. “There’s a whole continuum.”

3. Baseball will increasingly become an indoor sport.

If the Oakland Athletics move to Las Vegas, they’re all but certain to become the ninth Major League baseball team with at least the ability — if not the necessity — to play indoors.

In addition to the fully enclosed Tropicana Dome in Tampa Bay, seven stadiums currently have retractable roofs. And it is in the warmest, sunniest markets where those roofs most often remain closed: “Miami … played under an open roof just five times in the past two seasons — combined,” Fox Weather reports. The Rangers, meanwhile, replaced their only-26-year-old ballpark in 2019 because it had gotten literally too hot to play in Texas without air conditioning.

It’s not uncommon for the remaining open-air ballparks to top 95 degrees in the summer — a miserable experience for players and fans alike. Without covering more ballparks, injuries could climb and attendance could drop. “People might just say forget about it. I’m not going to a baseball game. It’s 105 degrees,” Brad Humphreys, professor of economics at West Virginia University, told Capital News Service.

4. It will speed up the robo-ump transition.

Triple-A baseball introduced electronic strike zones this season, fueling speculation that the controversial robo-ump system could be coming to the Major Leagues next. But there is one big reason in favor of electronic strike zones that doesn’t often get mentioned in the debate: climate change.

A recent study found that “umpires call pitches less accurately in uncomfortable temperatures, with performance at its worst in extreme heat conditions,” Monmouth University writes. Incorrect calls were made at a rate of about 1% worse when temperatures topped 95 degrees. And while that might seem insignificant, “it is non-trivial for this high-revenue, high-stakes industry,” the study’s author, Monmouth associate professor of economics Eric Fesselmeyer, said. “Moreover, high temperatures cause an even greater decrease in accuracy on close-call pitches along the edges of the strike zone.”

5. There will be more bench-clearing brawls.

Aggression and violence rise with the temperatures. In one study, violent crimes went up by as much as 5.7% on days with a maximum daily temperature above 85 degrees, and as much as 10% on days above about 88.

As dugouts and diamonds get hotter, tempers will too. But there is another reason to believe there will be more bench-clearing brawls beyond heat-induced short-fuses. According to a study published in the Personality and Social Psychology Bulletin in 1991, “a positive and significant relationship was found between temperature and the number of hit batters per game, even when potentially confounding variables having nothing to do with aggression were partialed out.”

Similarly, Duke University’s Fuqua School of Business found in 2011 that “pitchers whose teammates get hit by a pitch are more likely to retaliate and plunk an opposing batter when the temperature reaches 90 degrees than when it is cooler.” Curiously, if no one has been hit in a game, the study found “high temperatures have little effect on a pitcher’s behavior.” As one of the researchers put it, “heat affects a specific form of aggression. It increases retribution.”

6. Spring training facilities could move north …

Hurricane Ian — the category 4 hurricane that slammed southwest Florida last September — was the state’s costliest storm, inflicting $109 billion in damage including “totally” destroying 900 structures in Fort Meyers Beach alone. Among the damages: CenturyLink Sports Complex, the spring training facility of the Minnesota Twins; Fenway South, the Boston Red Sox’s facility; and Charlotte Sports Park, the Tampa Bay Rays’ spring training home, which sustained damage so extensive that the team had to find another stadium to practice in during the 2023 spring training season.

The lasting damage of the storm extends beyond the physical: “Hurricane Ian’s impact on Lee County likely played a role in depressing the crowds at Red Sox and Twins games this year,” Fort Myers News-Press reports.

There are no murmurs of moving the Grapefruit League’s spring training facilities — yet. But already the rising sea levels and storms of Florida are ruling out new stadium locations, including at least one potential regular-season home for the Rays. “Sites that once appeared to be great places to build a ballpark are now expected to be underwater,” the team president said. With climate already costing teams money and fans, as well as being a deciding factor in new builds, the Grapefruit League could prudently decide to uproot for higher grounds.

7. … As could team expansion.

Homebuyers are taking into account the future climate conditions of potential properties, and if MLB is wise, it will do the same when considering team expansion.

From a climate standpoint, it already seems egregious to move a team to a desert city that is running out of drinkable water in the summer, though the Oakland A’s potential relocation to Las Vegas is still very much on the table. But when MLB looks at locations to expand to — Portland, Mexico City, North Carolina, Nashville, Montreal, and Vancouver have also been floated — the climate calculus becomes ever more important.

In 60 years, Portland will have a climate similar to Sacramento, complete with the threat of wildfire smoke. Mexico City is getting hotter, drier, and sinking. Charlotte and Raleigh will eventually “resemble the Florida panhandle, specifically Tallahassee, which is 12.6 °F warmer and 10.6% to 14.4% wetter than winter in Charlotte and Raleigh. Nashville is not too far, with Mobile, Alabama serving as its closest projection,” Fangraphs writes in an assessment of the future of ballparks in the climate crisis.

Unsurprisingly, with an eye for the future, it is the northernmost cities that look like the best options to withstand climate change impacts: “Vancouver and Montreal could look toward current day T-Mobile Park and Citizens Bank Park as examples of how to keep fans comfortable during games.”

8. Players will need to learn to love turf.

Over the course of 12 months between 2019 and 2020, 10% of MLB teams switched from real grass to turf. “The three stadiums that replaced their grass share a lot in common,” wrote The Wall Street Journal at the time: “They play in cities with extreme weather and have retractable roofs.”

In Arizona, for example, real grass required sunlight — and thus an open roof — until between 4 p.m. and 7 p.m., which meant that players often worked out before games in temperatures of 110 degrees or more. By the time fans arrived, the building would still be sweltering, air conditioning not having yet kicked in. But by switching to turf, “the roof can remain closed all summer.”

Switching to turf also eliminates the demands of watering: Conservatively, about 62,500 gallons of water a week are required to maintain an average field, an amount 89 homes would use in the same amount of time. Though that water is likely negligible in the grand scheme of things, it’s important for teams to take “social responsibility” by “walking the walk,” Diamondbacks president and CEO Derrick Hall told The Associated Press.

Turf remains controversial — it can affect the bounce of balls and result in higher rates of injuries. Recent advances in turf technology, though, are making it more appealing for teams and the planet.

9. Say goodbye to giveaway days.

Anyone who’s ever watched nine innings of live baseball knows the kind of mess fans leave behind: peanut shell piles; beer cups; burger trays; plastic ice cream bowls shaped like hats; abandoned bobbleheads. Overall, baseball audiences create more than 1,000 tons of waste every season, according to the Green Sports Alliance.

A growing number of stadiums are now aspiring to contribute less to landfills, including by using compostable serving items and reducing food waste. But one place waste is still frequently overlooked is in promotional giveaways.

Every year, MLB gives away around four million bobbleheads in addition to other tchotchkes like branded visors, T-shirts, sunglasses, and bags. While some of these end up as treasured pieces of home collections, the vast majority are junk destined for landfills.

Though teams show no sign of forgoing giveaways anytime soon, the more environmentally conscious parks may begin to consider new ways of reducing their waste — including by curbing handouts of cheaply made petroleum products and environmentally taxing garments that no one actually needs.

10. The IL will get more crowded.

Every year, athletes end up on the Injured List for reasons ranging from benign to ridiculous. Now there is a new reason to be pulled from a game: heat illness. During one 2018 game at Wrigley Field with a heat index of 107, four players ultimately left the field for temperature-related causes, including three who had to be treated with IV fluids. During another game in 2021, a 28-year-old pitcher vomited on the mound in New York City. Diagnosis? Heat exhaustion.

Normal sports injuries also spike as it gets warmer. “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,” a former Rangers trainer told The Atlantic in 2016, prior to the construction of the team’s new air-conditioned stadium. “Our staff attributed that to the excessive heat and the fatigue.”

The prevalence of naturally occurring injuries could go up too because as players get dehydrated, their brain, thought capacity, and reflexes “are affected and the player is not able to react immediately on the field,” a 2021 study by the International Journal of Physical Education found. “The player will be injured due to a fall or collision with another player or being hit by a ball.”

Tragically, rising temperatures also are known to contribute to an increased number of deaths, a pattern already observable in high school football. Baseball fans and minor league athletes have already died due to heat-related causes — an awful pattern that isn’t likely to abate.

11. Statistical comparisons will need a climate-change asterisk.

In 2017, the mercury during the first game of the World Series in Los Angeles hit 103 degrees after 5 p.m.; the same year, the Oakland A’s Triple-A affiliate played in 111-degree heat in Las Vegas. On average, the temperature across the 27 Major League Baseball cities has risen over two degrees since 1970. And “the difference in home run rates between a 90-degree day and a 40-degree day is roughly equivalent to the difference between hitting in Citizens Bank Park” — which is small — “versus Citi Field,” which is comparatively huge, ESPN reports.

In our hotter, damper future, baseball will be a markedly different game than it was 50 years ago — or even now. Heat will affect players’ reflexes and focus. Balls will move differently through thinner, warmer air. Fielding could change ever so slightly as turf becomes more common, and pitchers might switch up their pitches as electronic strike zones come into use and curveballs become less effective.

All good statistical comparisons need context, and that is especially true in the ever-changing sport of baseball. But in the next century of the sport, it is all but certain that the literal environment of the games — from the weather to the air density to the AQI — will be a necessary asterisk beside unusual home runs and IL designations. One day, announcers may even reminisce about “open air” stadiums from their climate-controlled booths during downtime on broadcasts. Perhaps we’ll even have a name for the days of comparatively thicker air: the “cool-ball era.”

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  • Jeva Lange

    Jeva is a founding staff writer at Heatmap. Her writing has also appeared in The Week, where she formerly served as executive editor and culture critic, as well as in The New York Daily News, Vice, and Gothamist, among others. Jeva lives in New York City. Read More

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