Rising Heat Puts Marathon Performance Records at Risk

A new study shows that climate change is shrinking the window for record-breaking performances in world marathons. Released just before the New York City Marathon, the research reveals that increasing global temperatures are creating tough conditions for elite runners.

Athletes and coaches are becoming more concerned that warmer weather may permanently change the sport. The recent Berlin Marathon, for example, was run in unusually warm weather of 75 degrees Fahrenheit, far above ideal temperatures for peak performance.

The study, conducted by the U.S.-based non-profit organisation Climate Central, analysed 221 major global marathons scheduled for 2025. It found that 86% of them are expected to see a reduction in optimal running conditions by 2045.

This includes all seven Abbott World Marathon Majors — Boston, London, Berlin, Chicago, New York, Tokyo, and the newly added Sydney Marathon. The researchers warn that rising temperatures will make it increasingly difficult for runners to achieve top results.

Mhairi Maclennan, the fastest British female finisher at the 2024 London Marathon, said the findings highlight a serious problem for professional runners.

“At the elite level, conditions make or break a performance,” she explained. “We train for years, controlling every detail of our preparation, only to see ideal race temperatures becoming rarer. Climate change isn’t just about discomfort — it’s about losing the chance to reach our best.”

Maclennan’s comments reflect a growing awareness among athletes that global warming is not a distant issue but a daily challenge.

The report also defines the ideal temperature range for marathon runners, often referred to as the “sweet spot.” For male runners, the best performance occurs around 4 degrees Celsius (39 degrees Fahrenheit). For female runners, the optimal temperature is around 10 degrees Celsius (50 degrees Fahrenheit).

Unfortunately, global warming is pushing these ideal conditions out of reach. Tokyo currently has the best chance of providing these temperatures, with 69% of race days offering favourable conditions for men. However, even Tokyo is expected to see a major decline in suitability by 2045.

The report cites the 2025 Berlin and Tokyo Marathons as examples where heat waves have already raised temperatures beyond the best range for athletes. Race organisers have tried solutions such as starting earlier in the morning, but such adjustments can only offer small improvements.

In some cases, the heat has led to runners dropping out mid-race or finishing with slower times, showing that even minor increases in temperature can significantly affect endurance performance.

Kenyan legend Catherine Ndereba, a former world record holder and four-time Boston Marathon winner, said that runners are already learning to adapt.

“Climate change has altered the marathon,” Ndereba said. “Dehydration and exhaustion are now real threats. Even small mistakes in pacing or hydration can end a race early. Every step now carries a message — if we don’t protect our planet, even our strongest athletes will fall short.”

Her words remind the sporting world that performance depends not only on physical strength but also on the environment.

Ibrahim Hussein, the first Kenyan to win both the New York and Boston Marathons, echoed Ndereba’s view. “The climate is part of the course now,” he said. “If we don’t protect it, the records of the future and the enjoyment for all will fade.”

For these veteran runners, the issue goes beyond sports. It’s about preserving the health of athletes, fans, and cities that host these iconic events.

Climate experts warn that without significant action to limit global warming, many major marathons could become slower, more dangerous, or even harder to host. Runners may face more cancellations, heat-related illnesses, and rising safety risks.

The report calls for organisers to consider more sustainable race planning, such as greener energy use, better heat safety protocols, and flexible scheduling based on temperature forecasts.

The findings serve as a clear message that climate change is not just an environmental problem — it’s a sports issue, too. Marathons, often symbols of endurance and human strength, are now under threat from the very climate they depend on.

For athletes like Maclennan, Ndereba, and Hussein, every stride now carries a purpose beyond competition — to protect the environment that makes those achievements possible. Without global action to curb rising temperatures, the dream of breaking future marathon records may soon fade into history.