Is warmer weather a home run?

Courtesy Martin Pechy

HOUSTON – You may have heard about a recent Dartmouth study of major league home runs increasing by 500 from 2010 to 2019. That’s about a 1% increase from the average and a trajectory to 2100 would increase homers to an additional 467 per season! The premise is pretty simple: warmer air is less dense than cold air. So a baseball has a better chance of flying over that fence in a warmer environment given less drag. So in our warmer world, more home runs.

Dartmouth doctoral student Christopher Callahan authored the paper with others, and wasn’t really surprised by the results saying that this basically goes hand-in-glove (sorry) with our understanding of the physical world.

There was a glancing nod to the fact that Major League Baseball encourages long-ball hitters as the most effective way to score (and, let’s face it, home runs are exciting!). So more home runs can be attributed to much more than the weather and, for now, these numbers (50 out of 5,000 home runs per year) are pretty statistically insignificant. But that trajectory to 10 times the number gets my attention. To get their results, the authors used observations from 100,000 MLB games and 220,000 individual batted balls to show that higher temperatures substantially increase home runs.

The study’s full abstract is here in the American Meteorological Society bulletin, which certainly gives it credibility. The suggested turnaround, if we don’t want all these warm weather homers, is to play at night when it’s cooler or in domed stadiums which are temperature-controlled.

One factor left out of this study is humidity. I blogged about baseballs traveling farther in more humid environments a few years ago. The fact is, the molecular weight of air full of water (H2O) is LESS than that full of dry air (lots of oxygen and nitrogen) the lighter, humid air allows a baseball to go farther.

Why would this matter? Well, a daytime game played in warmer weather may well allow the baseball to go father, but if the weather is also humid, then that baseball would go farther still. I think the study needs to compare games played outdoors in Phoenix (hot and dry) versus games played outdoors in Tampa (warm and humid). The authors of this paper state relative humidity has only a minor effect on air density.

Well, you can have a look at my blog right here and come to your own conclusions. From what I could find, baseballs travel farther in warm, humid environments versus cold, dry environments. So comparing warm and humid to warm and dry may have some merit. After all, two feet can make a big difference in baseball!

At the end of the game, though, this study brought additional attention to our warming world in an interesting and understandable way and that is a subject that needs to be on deck as often as possible.


Email me with comments or questions!

About the Authors:

KPRC 2's chief meteorologist with four decades of experience forecasting Houston's weather.

Amanda Cochran is an Edward R. Murrow award-winning journalist. She specializes in Texas features, consumer and business news and local crime coverage.