Too hot, too humid, too wet to play: a first global climate-risk map for outdoor sport

What is it about?

Outdoor sport lives and dies by the weather, and the weather is shifting. Heat collapses in marathons, medical time-outs in tennis, football matches moved to winter — these aren't freak events, they're early signs of a structural change. Most research so far has looked at a single problem, usually temperature, in today's climate. We built the first worldwide picture that looks ahead and combines four hazards that actually stop people playing: Heat and humidity together (measured with WBGT, the same heat-stress index federations like FIFA and the ITF already use to postpone play) Dangerous heat more broadly (the "danger" level of the Heat Index) Heavy rain that waterlogs pitches and forces cancellations Heatwaves — multi-day hot spells that wear athletes down even when no single day is extreme Using fine-scale global climate model projections, we mapped all four across the whole planet for three periods — today, mid-century (around 2050), and end-of-century (around 2100) — under both a moderate and a high greenhouse-gas pathway. We also split the day into morning, afternoon and evening, because shifting matches to cooler hours is one of the main tools organisers have. Finally, we rolled everything into a single 0-to-1 score, the Sport Climate Risk Index (SCRI), to show where several problems hit at the same time. The headline results: safe conditions shrink fast. Under high emissions, large parts of the tropics and subtropics face two to three months per season above the heat-stress level at which competitions are normally suspended. The "cool morning" escape hatch closes in many densely populated regions, because mornings get dangerous too. And regions long assumed to be "climatically safe" — the Mediterranean, the southern US, eastern China — start crossing thresholds they almost never hit before.

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Photo by Simon Kessler on Unsplash

Photo by Simon Kessler on Unsplash

Why is it important?

This gives sport federations, event organisers, schools, clubs, medical staff and city planners a concrete evidence base to plan with — which calendars, venues and safety protocols still make sense, and where. Three practical messages stand out: Rescheduling helps, but it runs out of road. Moving activity to cooler hours works today, but in the hottest regions the whole day eventually exceeds safe limits, so time-of-day tricks alone won't be enough. It's not just heat. Rain and multi-day heatwaves add constraints that heat-only studies miss — sometimes overlapping into compound "hot and wet" hazards. Emissions choices decide the outcome. The gap between the moderate and high pathways is huge by late century. Under strong mitigation, the constraints are manageable with adaptation; under high emissions, large parts of the warm season become incompatible with safe outdoor sport in major regions. Cutting emissions isn't only an environmental goal — it's what determines whether outdoor sport stays viable in its traditional form.

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