How heat and home runs are connected

This exercise is a part of Educator Guide: Climate Change Spikes Baseball Homers / View Guide

Directions for teachers: Ask students to read the online Science News article “Baseball’s home run boom is due, in part, to climate change,” and have them answer the following questions. A version of the article, “Climate change spikes baseball homers,” appears in the May 6, 2023 & May 20, 2023 print issue of Science News.

1. What is sabermetrics? How can sabermetrics be used?

Sabermetrics is the study of baseball statistics. Teams use sabermetrics data to improve strategy, but this study demonstrates that the data also can be used in quantitative scientific studies.

2. In one sentence, state the scientific question Dartmouth’s Christopher Callahan and his colleagues asked in their research.

Has human-caused climate change contributed to the increase in the number of home runs hit during Major League Baseball games?

3. In what ways did researchers investigate the relationship between the increase in temperature and the increase in home runs, and what did they find?

After looking at more than 100,000 MLB games, the researchers concluded that the number of home runs increased by almost 2 percent when the daily high temperature increased by 1 degree Celsius. The researchers estimated that, from 2010 to 2019, there were an average of 58 home runs per season that could be attributed to human-caused climate change. When researchers looked at the results for 220,000 batted balls, where they accounted for temperatures, wind speed and humidity, the scientists found that home runs increased with temperature.

4. What factors did researchers control for in their studies? Were there factors that the researchers could not control for given the study design?

Researchers used the Statcast system to analyze 220,000 individual batted balls and studied those that were hit in the same way (a controlled factor), but the temperatures were different on the days the balls were hit. By looking at balls that were hit in the same way, the scientists were controlling for ball speed, pitch type and contact location. The article also said the researchers controlled for wind speed and humidity. What is hard to know is how much improvement in batter abilities have contributed to the increase in the number of home runs over time. Are batters simply better today than they were in the past?

5. Explain why it makes sense that as air temperature increases, more home runs are hit. From the article, extrapolate the chain of cause and effect.

Hit baseballs follow the rules of physics. Is this study, the ideal gas law provides an explanation for the scientists’ results. The ideal gas law says that when temperature goes up, air density drops. When air density drops, air resistance also drops. As air resistance declines, it becomes easier to hit a baseball a longer distance. Therefore, the number of home runs hit should increase with higher temperatures and lower air density, which is what the scientists found.

How could MLB mitigate the effects of climate change on the game?

MLB could decrease the number of day games and increase the number of night games; MLB could build more domes over stadiums.

7. What questions do you still have about the research described in the article?

It’s not clear to me how the researchers controlled for factors such as wind speed and humidity during the study. I also don’t understand how the researchers got to an average of 58 more home runs a season from 2010 to 2019 by running game-day temperatures through a climate model.

8. What’s another scientific question you could ask using sabermetrics?

Student answers will vary but could include questions about the relationship between the time of day, temperature and number of hits or the speed of the ball pitched, temperature and the number of strikes. A sample scientific question: In afternoon and night games when temperatures are the same, do players average the same number of hits in the earlier and later games?