The Running Clock: How Climate Change is Stopping the Stopwatch
A new scientific look suggests a worrying future for long-distance running.
The reason, climate change is fast cutting down on the number of cool days when marathon runners can really crush records.
The scoop, from Climate Central, says that more hot days are becoming a pain for top athletes and those putting on the big marathon races.
The report, called Running out of cool days:
How climate change is decreasing the odds of optimal marathon conditions, came out just before the New York City Marathon. It shows the planet getting hotter is messing with the cool weather that runners need to hit their best times.
A big climate study paints a grim future for the world’s best long-distance races. It figures most marathons will have way fewer days with perfect running weather in the next 20 years.
The study checked out 221 races around the world and says around 86% of them; about 190, are expected to have worse weather by 2045. This could stop runners from breaking records on a global scale.
All the Big Marathons Will Feel It
The races in Tokyo, Boston, Berlin, Chicago, London, New York, and Sydney are all going to have warmer weather that isn’t great for runners.
Tokyo’s Sweet Spot is Getting Smaller
Right now, the Tokyo Marathon has the best chance of having perfect race weather at 69%.
But, this good thing is going away quickly. If we keep pumping out emissions like we are now, there is a 12% chance of good temperatures dropping in Tokyo by 2045.
A new climate check shows that female athletes don’t feel the heat as much as male athletes do. But, specialists are warning that even a little bit of warming can hit world-record times and put runners in danger.
The study says that because top women do better when it’s warmer, they are not as bothered by climate change. For example, today the Tokyo Marathon has a 78% chance of perfect race temperatures for top female runners. It’s expected to jump to 85% by 2045.
Marathon Weather: It’s Getting Weird
A recent study looked at weather patterns in major marathons, and things are changing. London’s looking good for top women runners right now – there’s a pretty good chance (87%) the temperature will be ideal.
But Berlin? Not so much. The odds of perfect weather for those runners could go down from 40% now to just 29% by 2045.
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Crazy Heat and Climate Change
The study says climate change is to blame for the recent hot weather at marathons. They mentioned the super-hot 2025 races in Tokyo and Berlin, where it was way too warm for runners, pros or amateurs. The study found that climate change was a big reason for those crazy temperatures.
Basically, some scientists checked out how climate change is messing with marathon weather. They used the Climate Shift Index (CSI) to see how much climate change was responsible. Turns out, those hot races weren’t random – global warming played a big part.
Run of fire Tokyo
Back on March 2, 2025, during the Tokyo Marathon, the temperature hit 15.2°C (59.4°F). That’s about 8.2°C warmer than usual for that day. The CSI was at 3, meaning climate change made that heat three times more likely!
Berlin’s race of fire
A similar thing happened at the Berlin Marathon on September 21, 2025. The temperature was 20.7°C, about 6.7°C warmer than average. The CSI was at 2, meaning global warming doubled the chances of that heat.
Climate Central said it well: Heat waves are already messing with marathon records… What used to be awesome racing weather is becoming rare. Things are changing.
And another thing the climate check showed? Top women runners can handle hotter temperatures a bit better than men. But even a little bit warmer can mess with their performance and, more importantly, safety.
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London vs. Berlin: Two different races
The study shows how different things could be for women running in different major marathons.
London’s looking nice, with that 87% chance of great temperatures.
But Berlin’s not so lucky. The chance of ideal race conditions could drop from 40% to just 29% by 2045.
Tokyo’s in a weird spot, too. The odds of good temperatures for women might improve a bit, from 78% to 85% by 2045, but there’s a higher chance of crazy heat waves.
Climate Change: Here and Now
The report says this isn’t a future worry – it’s happening now. The crazy heat at the 2025 Tokyo and Berlin Marathons is a clear example, where climate change made those dangerous temperatures more likely.
Tokyo 2025: The temperature on race day was 15.2°C (59.4°F), a crazy 8.2°C warmer than normal. The CSI was 3, meaning climate change made the heat three times more likely.
Berlin 2025: The race had an average temperature of 20.7°C, around 6.7°C.
Warmer than usual, with a CSI of 2 – twice as likely because of global warming.
Like Climate Central said, Heat waves are already changing marathon races. Great race weather is becoming rare, which means we need to rethink how we plan races and prepare athletes.
