On 23 September 2026 The Guardian reported on a Climate Impact Lab study that attempts, for the first time, to quantify in advance the mortality consequences of an El Niño event while it is still unfolding. It estimates that the additional heat of the 2026 super El Niño could cause some 451,000 excess heat-related deaths worldwide between June 2026 and February 2027. The figure excludes the victims of the droughts, wildfires and floods that accompany El Niño, and it comes on top of the deaths already caused by temperatures raised by climate change.
The report is co-authored by Professor Michael Greenstone (University of Chicago) and Dr Tamma Carleton (University of California, Berkeley). Its method rests on peer-reviewed techniques: the month-by-month relationship between temperature and excess mortality was established for 24,378 regions and combined with forecasts of El Niño-driven warming. The baseline is the average month of 1996–2025. The report has yet to complete peer review; Greenstone said that, given the urgency, it would have been irresponsible to sit on it. The estimate is therefore preliminary – but its order of magnitude is not in doubt.
In Hungary, too, heat causes hundreds of deaths every summer – in some years more than a thousand
These are epidemiological model estimates: from daily temperature and mortality series they calculate the excess mortality attributable to heat. As individual causes of death these cases rarely appear – heat typically kills through the fatal aggravation of existing cardiovascular and respiratory disease. That is why heat mortality remains largely invisible to the public.
The 2026 event: record heat months before the peak
In the second half of September, several months before its expected peak, the current El Niño passed the highest temperature ever recorded for the phenomenon. The excess heat so far exceeds that of earlier events that scientists have called it “mind-blowing” and “Godzilla-level”. In the words of Professor Friederike Otto (Imperial College London), the event is a huge redistribution of energy in the climate system, and it is dangerous because it is unfolding on top of a much warmer, human-influenced climate.
The countries projected to be worst affected are the tropical nations of Nigeria, Indonesia, Sudan, India and Brazil; more broadly, the Sahel and south-east Asia. The United States is among the twenty worst affected, with 3,500 projected extra deaths. According to the researchers, elevated heat mortality may persist until June or July 2027 – long enough to cover a full northern-hemisphere summer. El Niño also strikes at food supply: in August the UN World Food Programme warned that its impacts could push about 50 million people into acute hunger.
The authors describe the event as a “postcard from our future”: El Niño is delivering now the temperature level that climate change, on its present trajectory, is projected to make normal in about twenty years. That observation is what turns the question into one of building energy performance. The buildings constructed and renovated today will serve precisely that climate, typically for half a century or more.
Emergency response saves lives – but it is not a strategy
The practical purpose of the Climate Impact Lab’s regional estimate is to direct protection where it can save the most lives: better heat forecasts, cooling centres, increased medical staffing at the hottest times and protection for outdoor workers. In Hungary the counterpart of this system is the national Chief Medical Officer’s heat alert and the local-authority measures attached to it.
These measures demonstrably reduce mortality, but they share one limitation: they operate during hot days and leave unchanged the environment in which people endure the heat. Tamma Carleton put it this way: emergency response can save many lives this year, but twenty years from now, once today’s extremes are the new normal, “we don’t want to be in a constant state of emergency”.
From a building-physics standpoint that is an accurate diagnosis. Most heat-related deaths occur not in the street but indoors – at home. The French epidemiologist Sandrine Vandentorren and her colleagues compared older people who died at home during the 2003 European heatwave with those who survived; their results, published in the European Journal of Public Health in 2006, identified a bedroom directly beneath the roof and inadequate thermal insulation of the dwelling as independent risk factors. In the 2024 European data the heat-related mortality rate among the over-75s was 323% higher than in all other age groups – highest, in other words, among those who spend most of the day at home and whose bodies are least able to compensate for heat stress.
Why heat mortality is a question of building physics
Indoor heat stress is not simply a consequence of the outdoor temperature. It is determined jointly by heat gain through the building envelope, solar radiation entering through the glazing, the thermal mass of the structure and the opportunity for night-time cooling. The critical factor is not the daytime peak but the night: if the indoor temperature does not fall after dark, the body cannot recover, and heat stress accumulating over several days can become fatal for older and chronically ill people.
The building stock is sharply stratified in this respect. Particularly exposed are top-floor flats, where heat gain through the roof and the walls combines; lightweight buildings and lightweight loft conversions with little thermal mass; and dense inner-city blocks, where the urban heat island suppresses night-time cooling as well. A large share of heat victims live in exactly these spaces.
Mechanical cooling is effective protection for the individual, but at system level it has three limitations. The most vulnerable households are often those that cannot afford the equipment or its running costs. Air conditioning creates a peak electricity demand that coincides with heat peaks – precisely when the grid is most fragile. And the waste heat from outdoor units reinforces the urban heat island. The durable answer is therefore passive building-physics intervention that reduces heat gain in the first place and allows mechanical cooling, where it is needed, to be sized smaller and run for fewer hours.
Where GWR NANO INSULATION® fits, and where the data stop
Conductive heat transfer works in both directions: an envelope element that lets less heat out in winter also reduces the conductive heat flow inward in summer. The thermal performance of GWR NANO INSULATION® measured in the heating season is documented in TÜV SÜD external monitoring report no. 3229268. In the comparative field test at Dunabogdány – measured by the testing and calibration laboratory of MEOLIT Kft. in January and February 2021 on three identical test houses – the coated house used 43% less heating energy than the uninsulated house and 9.5% less than the reference house with 10 cm of EPS insulation.
No quantitative conclusion about summer performance can be drawn from this, and the point needs stating precisely. In summer heat stress, beyond conductive heat flow, the solar radiation absorbed at the external surface and the thermal mass of the structure play a decisive part. The coating’s solar reflectance and solar reflectance index (SRI) have not been measured, and a 1 mm dry film does not materially change the thermal mass of the structure. No independent measurement of summer indoor temperatures equivalent to the heating-season test exists, so this analysis gives no summer percentage. The scope of the report is limited for the winter data too: the report does not regard its own Dunabogdány field measurement as an internationally standardised procedure.
What speaks for the coating is the application side – and in heat protection that matters especially. The most exposed parts of the stock – top-floor flats, articulated inner-city facades and occupied buildings – are exactly where board insulation often cannot be built or scheduled. The coating is applied by airless spray, on low- and medium-rise buildings typically without scaffolding, and the building can stay occupied throughout – which, for older residents, is a matter of health rather than convenience. The coating remains vapour-permeable (sd = 0.40 m, class V2), so it does not block outward drying of the wall. Where external board insulation can be built, it delivers the greater and better-documented reduction in heat loss; and in summer heat protection, shading, roof insulation and designed night-time purge ventilation are prerequisites in every case.
Engineering conclusions
The 2026 El Niño estimate points to three conclusions for the management of the building stock, each building on the last.
- In public-health terms: most heat-related deaths occur indoors, so the thermal protection of the building stock is a public-health factor. Heat alerts and cooling centres save lives, but they reduce the risk only temporarily; it is only the living environment itself that changes it durably, summer after summer.
- In design terms: El Niño is delivering now the climate that, on the present trajectory, becomes normal in two decades. The buildings renovated today will serve that climate, so summer overheating has to be treated as a design task on a par with winter heat loss.
- In building-physics terms: improving the thermal protection of the envelope reduces both winter heat loss and conductive summer heat gain. Summer indoor temperatures, however, also depend on the solar radiation absorbed at the external surface, the thermal mass of the structure and night-time ventilation, so summer thermal performance can be demonstrated only by summer measurement. The thermal performance of GWR NANO INSULATION® is currently documented only by independent measurements taken in the heating season.
A heat-related death is a preventable death. The most effective means of preventing it is not the alert, but a home that does not become life-threatening on the third night of a heatwave.
The climate mechanisms of the 2026 super El Niño and its effect on European cooling demand are examined in our analysis of building envelope resilience during El Niño, and the links between heat, drought and the energy system in the post on the EU hydrological drought. The planning order of envelope and building services is set out in our post on heat pump retrofits. Documented installations in Hungary and abroad are set out, project by project, on the References page.
GWR NANO INSULATION® is distributed in Hungary and the Central and Eastern European region by Summotive® (Summa Technologiae Kft.). TÜV SÜD test reports, the Declaration of Performance, and technical data sheets are available on request.