Winning times for the Boston Marathon have grown steadily faster over the past 80 years, with
better training methods and an increasing number of international runners. Winning times may
nonetheless slow in the future as the climate of Boston continues to warm—running times
are already affected by weather on the day of the race. For example, the winning men’s time
during last year’s hot weather was nine minutes slower than it had been in the cool-weather race
of 2011. Our analysis shows that winning times are almost 2 minutes slower for every 10⁰ F
increase in temperature. The main reason that heat so often beats runners is its adverse effects
on the human body’s ability to regulate internal temperature, leading to heat exhaustion, cramps,
dehydration, and other injuries.
Even though Boston’s average annual temperatures have steadily warmed by about 5⁰ F over
the past 80 years, the average temperature on race day has not changed so far because of the
great variation in the weather from day to day in Boston. The temperature for the 2012 race, for
example, fell only one degree short of the all-time high at 89⁰, while in 2011 it was a chilly 57⁰.
As a result, global warming has not yet affected winning times of the Boston Marathon. But what
about the future?
Based on our research, if Boston temperatures continue to warm by 4.5⁰ F by the end of the
century as predicted using a mid-range model, there will be 64% chance that winning times
will be slower. If the shift is as high 9.4⁰ F, which is an upper estimate of global warming, the
probability of slower race times is bumped up to 95%.
Warming temperatures have implications not only for the Boston Marathon, but for the future of
all warm-weather outdoor activities, including construction and farm work, team and endurance
sports, and physical fitness training.