Sport wrote new heat rules for 2026. Cooling researchers call them small

2026 is the year competitive sport started writing heat into its rulebooks. FIFA made a three-minute hydration break mandatory in every World Cup match regardless of conditions [s3]. The ATP adopted its first formal heat policy, keyed to wet bulb globe temperature [s6]. Both changes are new, both are real, and researchers who study human thermoregulation say both are calibrated below what the physiology requires.

The background number

The context is not abstract. On 13 July 2026, the Met Office, Imperial College London, the London School of Hygiene & Tropical Medicine and the UK Health Security Agency published modelled estimates of heat mortality in England and Wales for the first two heatwaves of the year [s1]. About 550 people are estimated to have died from heat-related causes during the 21-29 May event and about 2,200 during the 18-28 June event — more than 2,700 in total [s1].

The attribution analysis estimated that 42% of those deaths across both heatwaves would not have occurred without human-caused climate change, with the split uneven: 59% of the May deaths and 38% of the June deaths [s1]. Human-caused warming added an estimated 3 to 4°C to maximum temperatures [s1]. West London recorded 35.1°C in May, breaking a record standing since 1944; East Anglia exceeded 37°C in June, breaking a June record standing since 1976 [s1].

Mark McCarthy, who manages climate attribution at the Met Office, said "2026 has been exceptional for the two early season heatwaves", and that human-caused climate change is producing more frequent and more intense summer heatwaves [s1]. Malcolm Mistry, assistant professor in climate and geo-spatial modelling at LSHTM, described these events as "rapidly evolving into a major health risk" [s1]. These are modelled estimates, not death certificates, and the release presents them as such [s1].

The relevance to sport is that both events fell in May and June — before the traditional peak of summer heat, and squarely inside the competitive calendar.

What FIFA implemented

FIFA announced on 7 December 2025 that referees would stop play 22 minutes into each half of every 2026 World Cup match for a three-minute hydration break, whistle to whistle [s3]. The rule is unconditional. Manolo Zubiria, FIFA's chief tournament officer for the United States, put it directly: "For every game, no matter where the games are played, no matter if there's a roof, (or) temperature-wise, there will be a three-minute hydration break" [s3].

Making the break universal removes the discretion that previously governed cooling stoppages, which is a genuine improvement over threshold-triggered breaks that depend on someone deciding a threshold has been crossed. The dispute is over the dose.

Ahead of the tournament, researchers including Douglas Casa, chief executive of the Korey Stringer Institute and Board of Trustees Distinguished Professor of Kinesiology at the University of Connecticut, and Robert Huggins, the institute's chief research officer and an assistant professor of kinesiology, signed an open letter urging FIFA to lower its wet bulb globe temperature threshold from 32°C to 26°C, extend breaks from three to six minutes, and provide air-conditioned locker rooms to all teams [s4]. Their stated principle: protocols that "prioritize prevention over response, and that align with contemporary exercise physiology, occupational health principles, and duty-of-care standards expected in elite sport" [s4]. Huggins framed the practical problem as one of exposure duration: "These athletes are playing for an hour or an hour and a half of with no break besides halftime" [s4].

What cooling actually does

Scientific American canvassed researchers in June 2026 on which interventions have evidence behind them [s2]. The answers are unflattering to most of what is visible on television.

Ollie Jay, professor of heat and health at the University of Sydney, made the observation that undercuts the break format itself: "They're taking these breaks in the sun" [s2]. Julien Périard, director of the University of Canberra Research Institute for Sport and Exercise, said halftime spent in an air-conditioned room is "far better" than a three-minute pause on the field [s2]. Lee Taylor, a sports performance expert at Loughborough University, characterised the breaks as "proven to be more of a commercial opportunity" [s2].

On the equipment side, Jonas Werner, team physician for the Swedish national team, said ice bags and cold towels are "mostly for comfort" with "scarce" evidence behind them, because they chill skin rather than core temperature [s2]. Cooling vests marketed with claims of roughly 1°F core temperature reduction require 12 to 15 minutes of use to achieve it — "something no one does", per Werner [s2].

The intervention the researchers converged on was heat acclimatisation: training in hot conditions raises blood plasma volume and sweating capacity, which shifts an athlete's tolerance ceiling before competition rather than trying to reverse heat strain during it [s2]. Roughly a quarter of 2026 World Cup matches were expected to be played at wet bulb globe temperatures of 26°C or above [s2].

The clinical end of the spectrum

The reason thresholds matter is what sits at the far end of them. Sports medicine guidance for on-site medical staff defines exertional heat stroke by two criteria: a rectal temperature above 105°F (40.5°C) immediately post-collapse, and central nervous system dysfunction — irrational behaviour, irritability, emotional instability, altered consciousness, collapse or coma [s5]. Collapse itself is not required for the diagnosis [s5].

Two points from that guidance are worth stating precisely because they are widely misunderstood. First, rectal temperature is the measure the criteria are built on; oral, tympanic, axillary and forehead methods are explicitly not treated as substitutes [s5]. Second, the sequence is cooling first: guidance directs staff to begin whole-body ice water immersion — target water temperature roughly 35 to 58°F — and to activate emergency services after cooling has been initiated, ceasing cooling when rectal temperature falls to 101–102°F [s5]. The evidence underpinning that sequence is the observation that exertional heat stroke has had a 100% survival rate when immediate cooling was started within 10 minutes of collapse [s5].

That is a clinical protocol for trained medical staff with equipment on site, not general advice. Its relevance to the rules debate is that the difference between a manageable event and a medical emergency is measured in minutes of core temperature exposure — which is the same currency the break-length argument is denominated in.

Tennis took the threshold approach

The ATP's policy, effective from the 2026 season and applying at the four Grand Slams as well as tour events, works the other way from FIFA's: conditional rather than universal [s6]. At a wet bulb globe temperature of 30.1°C or above, either player may request a 10-minute cooling break after the second set of a best-of-three match; at 32.2°C, play is suspended [s6]. During breaks players may hydrate, change clothing, shower and receive coaching under ATP medical supervision [s6]. The WTA has used WBGT since 1992 [s6]; the men's tour adopted a comparable standard after seven players retired mid-match in heat and humidity at the 2025 Shanghai Masters, held 1 to 12 October [s6].

A 10-minute break with access to a shower is, notably, closer to what the FIFA letter's signatories asked for than what football adopted.

What to watch

Whether FIFA publishes any internal analysis of how the mandatory breaks performed across the tournament — core temperature or heat-illness incidence data would settle a lot of this quickly, and none has been made public. Whether the wet bulb globe temperature threshold for suspension moves closer to the 26°C the letter's signatories proposed [s4]. And whether governing bodies begin treating acclimatisation protocols as a scheduling matter rather than a team-level choice, since that is the intervention researchers rank highest and the one no current rule addresses [s2].

Sources

• [s1] More than 2,700 excess deaths estimated in England and Wales during May and June heatwaves — Met Office, 13 July 2026
• [s2] Which World Cup cooling methods really protect players from extreme heat? — Scientific American, 19 June 2026
• [s3] Players to benefit from hydration breaks at FIFA World Cup 2026 — FIFA, 7 December 2025
• [s4] UConn Experts Push FIFA to Protect Players from Extreme Heat — University of Connecticut, 9 June 2026
• [s5] Exertional Heat Stroke — Korey Stringer Institute, University of Connecticut (accessed 23 August 2026)
• [s6] ATP to introduce new heat policy in 2026 — Sport Resolutions, 17 December 2025