A new study by Climate Central reveals that global warming is increasingly reducing the likelihood of optimal running conditions at major marathon events worldwide, threatening athletes’ performance and record-breaking attempts. This research, analyzing 221 marathons, indicates that 86% of these races are expected to have fewer days with ideal temperatures by 2045 due to climate change.
The study defines optimal temperatures for elite runners as 39 degrees Fahrenheit (4 degrees Celsius) for men and 48 degrees Fahrenheit (9 degrees Celsius) for women, which minimize heat stress and allow peak performance. However, with 2024 being the hottest year on record, many recent marathons have already experienced unseasonably warm weather. For instance, the Berlin Marathon in September 2025 saw temperatures reach 75 degrees Fahrenheit (24 degrees Celsius), while the Tokyo Marathon averaged 59 degrees Fahrenheit, significantly above normal.
Future projections are alarming. The Tokyo Marathon, which currently has a 69% chance of optimal conditions for elite men, may see that probability drop to 57% by 2045. Similarly, the Boston Marathon’s odds could fall from 61% to 53%, and London’s from 22% to 17%. These declines are driven by the overall warming trend, with Climate Central noting that the unusual heat at the 2025 Tokyo Marathon was made three times more likely due to climate change.
The impacts extend beyond elite athletes to recreational runners, who face increased risks of dehydration, heat exhaustion, and longer recovery times. Scottish distance runner Mhairi Maclennan emphasized that heat can affect blood thickness, hydration levels, and training capabilities, potentially delaying personal goals. She highlighted that heat waves are already ‘rewriting race history’ by reducing opportunities for record-breaking performances.
Recent events underscore these challenges. At the Berlin Marathon, organizers advised runners to shift focus from personal bests to enjoying the atmosphere due to warm conditions, providing guidance on hydration and cooling strategies. Similarly, the New York City Marathon in November 2025 benefited from cooler weather, but such ideal conditions are becoming rarer.
In response, race organizers might need to adapt by scheduling earlier start times or adjusting race dates. An extreme example was the 2019 World Athletics Championships in Doha, where marathons began at midnight to avoid daytime heat, yet temperatures still reached 88 degrees Fahrenheit (31 degrees Celsius) with high humidity. Such measures highlight the growing need for innovation in event planning.
The broader implications connect climate change to sports and public health. Andrew Pershing, who led the Climate Central science team, explained that as the climate warms, the ‘good climate’ for running is shifting, making optimal conditions less frequent. This trend could lead to fewer record breaks and alter the historical narrative of marathon achievements, emphasizing the urgency of addressing global warming.
Ultimately, reducing heat-trapping pollution through renewables and emission cuts is essential to safeguard marathon events. Without action, the sport may face increasing hurdles in maintaining safety and performance standards, reflecting a wider environmental crisis affecting human activities.