Weekend Reads | Climate Change and Home Runs

by Kevin Schofield

You're probably already aware that climate change is predicted to have broad and severe effects on our world in the coming decades. In many places, we can already begin to see those effects, including rising temperatures, higher tides, and more extreme weather patterns. In some cases, they have impacted our daily lives, but a group of researchers from Dartmouth College recently published a paper analyzing one more of these impacts that you probably haven't spent much time thinking about: the number of home runs hit in Major League baseball games.

If you follow baseball, then you know there has been a substantial increase in home runs hit over the past decade, and there are a number of factors contributing to this. The way baseballs are manufactured is one of them, as Major League Baseball (MLB) keeps tweaking the specs for the materials and stitching — which led to a "juiced ball" era for some years. Also, the rise of baseball analytics, which have informed how both pitchers and hitters train and play, have led to more optimized swings, and with that, more batters "swinging for the fence." But how much of a difference does climate change contribute on top of that? The researchers collected data going back to the 1960s to try to answer that question.

For the first part of their analysis, they gathered data for over 100,000 MLB games from 1962 to 2019, including the temperature at the stadium during the game and the number of home runs hit during the game. They found that a 1 degree Celsius increase in temperature on the day of a game that was played in a stadium without a roof (or with a retractable roof that was open) increased the number of home runs hit by almost 2%. The increase was larger for "day games" played in the heat of the afternoon, and lesser for night games. Games played inside a dome or under a roof saw no difference in home run rate based on the temperature. Both home teams and visiting teams saw the same increase, and even excluding games played after 2000 (when the "juiced ball" and analytics eras have had the greatest impact), the effect is still there.

Diving further into the data, they found that even after accounting for precipitation, humidity, and wind speed, the effect of temperature on home runs still existed. But they determined that it wasn't the temperature itself that caused the increase; rather, it was that increasing the temperature decreases the air density — and balls travel farther in "thinner" air.

The effect of air density is well known to airplane pilots, as is the impact of temperature on air density. Pilots learn in training that thinner air means less lift and thrust, so they will need more runway to take off. That affects airplanes everywhere on hot days, but even more so at airports at higher altitudes. That's why Denver Airport, in the Mile High City, has a 16,000-foot runway — more than three miles long — so that large, heavy cargo planes can still take off on a hot July day (by comparison, Sea-Tac's longest runway is less than 12,000 feet).

This isn't entirely new information to MLB either. Coors Field in Denver, the home stadium of the Colorado Rockies, is well known as a "hitter's park" and a terrible place for pitchers to try to make a career. The Phoenix baseball stadium, home of the Arizona Diamondbacks, has a roof that closes up and seals the stadium so it can be air-conditioned, both for the comfort of the guests and to limit the effects of the desert heat on the game. But no one before has actually quantified how much of a difference to the home run count the air density makes, let alone predicted how much it will have an impact in the years to come.

The second part of their research study took advantage of a new data collection system called Statcast that was installed across MLB in 2016 and provides detailed statistics on every individual pitch and batted ball. That includes key details about a baseball both at the moment it leaves the bat and when it comes to rest, telling the researchers its "launch" angle and velocity and how far it traveled. With a combination of that data and weather information, they could look at the different outcomes for balls that were hit identically. They found that for each additional degree (Celsius) of temperature, there was a 1.83% increase in home runs. Based on that, they calculate that global warming led to 58 more home runs per year on average between 2010 and 2019.

Climate scientists have a range of predictions for the temperature effects of climate change in future years. Following the pessimistic scenario (i.e., greater greenhouse gas emissions), the researchers predict there will be an additional 192 home runs per year by 2050, and 467 more by 2100.

The paper includes a nifty chart showing predictions for increased home runs for each of the 30 MLB parks, depending upon how much global warming occurs. Seattle's T-Mobile Park is in the middle of the pack, while not surprisingly, Coors Field has nearly the largest increase in home runs. The most impacted park, however, would be Chicago's Wrigley Field (and it makes one wonder how all that ivy will hold up).

The researchers point out that there are things MLB could do to adapt to climate change that would limit the increase in home runs. They could dome all stadiums, or convert most or all day games into night games. They could also change the materials in baseball bats and alter pitching strategies.

They also note that "more home runs in baseball" is hardly the worst predicted effect of climate change, which is expected to flood inhabited areas, displace millions of people, cause droughts and famines, and wreak severe economic damage in some places. Nevertheless, it reminds us that climate change impacts will be broad and deep, with consequences both large and small to almost every aspect of our lives.

Global warming, home runs, and the future of America's pastime

Featured image by Mike Orlov/Shutterstock.com.