July was the hottest month worldwide ever recorded.

NOAA (The National Oceanic and Atmospheric Administration) says temps are rising about .07 degrees a year, causing dramatic localized weather and temperature swings. 

It’s obvious, times are a changin, but what does this really mean for all us runners out there? 

In months like this July were the mercury hit nearly 100 degrees across the country, we all most likely felt the added strain of training out in the heat.

A new study from RunRepeat, aimed to find out what actually happens to runners as temps rise and the findings are outstanding. The study looks at marathon finish times only, but for every degree of temp increase the average marathon runner loses about 1 minute 25 seconds.

RunRepeat analyzed 19.6 million marathon results from over 30,000 marathons around the world, and found that race-day temps are responsible for over 30% of the variance in finish times and as they go up they closely correlate to slower times. 

This is a major factor considering that more and more races these days are being held in warmer months where average race day temps top 60 degrees, well above the optimal race temps of between 42-43 degrees. 

You can see below the wide swing of temps the Chicago Marathon has seen in the last 18 years and how average temps have steadily been climbing. Over the last two decades the average temperature at the Chicago Marathon has risen by 5 degrees, which based on the data would be an additional 7 minutes and 5 seconds to the average racer’s finish time.

Finish times follow the raising temps trends, the hotter it is, the slower racers tend to be: 

The data looks similar from races across the globe too. Racers and race organizers need to be aware of the pressures temps create and as weather patterns begin to change, maybe so should future race dates. 

Avoiding the heat not only ensures your best shot at hitting your finish time goals, it’s also safer for runners. In 2007, the Chicago Marathon hit a record 88 degrees and ended early with around 50 participants hospitalized and one fatality. Be safe out there, know your limits, and know that these trends promise to continue as climate change speeds with us into the future.

Guest post provided by Paul Ronto – Director of Content at RunRepeat.com