Chris Pastore

Upper Dublin, PA

Baseball and Climate Change

The commentators on today’s baseball game spoke about the changes in ERA for professional baseball over the decades.  They gave averages per decade for the past 30 years.  This made me wonder about a more detailed view.

I went to and collected league average ERAs from 1944 until 2009 and plotted them, as shown below.

MLB average ERA vs time

Change in MLB average ERA as a function of time

It doesn’t appear to me that there is any clear trend here.  There is a low point in 1968, which is strange because the pitching mound was lowered in 1969 and I was expecting the low point there.

There does appear to be an increase in ERA from 1968 until 2009, but the highest ERA was in 1931.  So maybe there are just local fluctuations as pitching gets stronger and then batters catch up and then pitchers catch up, and so on.

This started me thinking about global temperatures.  I hear many discussions on whether or not the observed changes in temperature for the planet (average surface temperature, for example) are a clear trend or a fluctuation.  In many respects this is a key question for people trying to understand the human impact on temperature.

So for grins, I grabbed the global temperature as reported by NASA from 1944 until 2009.  Then I averaged the temperatures in the months May through September (baseball season) over this period.

The following graph shows the relationship between seasonal temperatures and league average ERA.

Correlation between global seasonal temperature and MLB average ERA

Correlation between global seasonal temperature and MLB average ERA

This appears to have a higher correlation than other graphs.

So although I don’t know what is causing global temperature changes, it does appear that warmer summers leads to better hitting!

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