Experts highlight a 'real risk' of hazardous conditions, particularly in Miami games, though risks vary across the 16 venues

North America faces a scorching summer ahead. The National Weather Service's 'seasonal temperature outlook' predicts above-average heat nationwide in June and July. Into this sweltering backdrop, 48 men's national teams will descend for the World Cup across the US, Canada, and Mexico.

The Guardian has conducted a detailed examination of the weather challenges awaiting players, comparing conditions to the 1994 tournament - when the US hosted alone - and pinpointing venues prone to extreme heat stress.

Key insights reveal that all Miami matches could surpass critical heat thresholds, and heat has intensified at every site except Mexico City's Azteca Stadium over the last 30 years. Scientists caution that numerous games pose dangers to athletes and spectators alike. Yet Fifpro, the international players' union, praises Fifa for addressing their worries and implementing health safeguards.

Intense heat combined with humidity hampers on-field performance. The wet bulb globe temperature (WBGT) metric evaluates this threat by factoring in air temperature, humidity, radiant heat like sunlight, and wind. Sports organizations rely on WBGT to set safe play limits; Fifa's protocols call for match suspension reviews at 32C WBGT pre-game. Fifpro advocates a stricter 28C cutoff.

A study in the journal Temperature this year analyzed last summer's Club World Cup: 31 of 57 games averaged over 28C WBGT. Performance stats showed higher WBGT correlated with reduced distances run by players at all speeds, including sprints. The authors stressed that heat stress impairs soccer players' physical output and underscored the need for protective measures to safeguard elite athletes' performance and well-being.

Drawing on World Weather Attribution (WWA) data, assessments indicate 26 World Cup matches may hit 26C WBGT or higher - Fifpro's cue for cooling breaks. At 28C, just five games are projected, but 45 carry up to 20% odds. For 30C WBGT, odds stand at one-in-four. Versus 1994, 26C exceedances jump 52%, and 28C cases rise 75%.

Theodore Keeping, lead WWA researcher and Imperial College London associate in extreme weather and climate, deems a 28C breach 'more likely than not.' He notes their projections might underestimate if temperatures spike or sunlight intensifies.

'An above-average anomaly would make estimates conservative,' Keeping explained. 'Direct sun adds another layer.'

'Half of human-driven climate change has unfolded since 1994's North American World Cup. The tournament climate has transformed dramatically in 32 years,' said Joyce Kimutai, another Imperial extreme weather researcher with WWA. 'Organizers have shifted high-risk games in uncooled spots like Miami and Kansas City to evenings, but unsafe conditions for players and fans remain a genuine threat.'

Houston, Dallas, and Atlanta - prime heat hotspots - boast air-conditioned stadiums, neutralizing indoor risks but not outdoor ones for fans. Fifa unveiled mitigations post-draw: evening starts in hot zones and mandatory three-minute cooling breaks per half. Further steps include boosted stadium cooling, a heat illness taskforce for uniform protocols, 'cooling bags' for treatment, and allowing full water bottles for spectators - unlike last year's Club World Cup.

Miami's stadium bucks the trend: none of its seven matches start after 7.30pm local time. Canada's Vancouver and Toronto venues rank low-risk, as do Mexico's three sites.

Ranking high-risk fixtures by team shows Uruguay facing two; Brazil, Cape Verde, Saudi Arabia, and Scotland one each. The USA enjoys low heat exposure across its trio.

A Fifa spokesperson stated: 'Fifa prioritizes health and safety for players, referees, fans, volunteers, and staff. Climate risks factor into planning, coordinated with host cities, stadium operators, and agencies.

'For elevated forecasts above thresholds, fans may bring one sealed water bottle; venues add cooling via shade, misters, buses, and water stations.

'Staff work-rest adjusts, first-aid ramps up with triage protocols for heat cases. Measures adapt to live conditions pre- and during events.'

Fifpro's spokesperson added: 'Clear efforts align scheduling and venues with player health and performance needs. Organizers adapted from lessons learned - essential amid warming. Heat will increasingly shape future tournament and league calendars.'