What summer 2026 actually measured.
The Met Office confirmed that Cardiff Bute Park reached 35.9°C in late June 2026, the highest June temperature on record for Wales. That is not the all-time Welsh record, which remains 37.1°C at Hawarden in Flintshire, set in July 2022, but it is the hottest June day Wales has ever measured. The overnight minimum during the same spell reached 23.5°C across parts of the UK, which matters as much as the daytime peak, because a house that cannot cool down at night is the one that becomes genuinely hard to live in.
By mid-July, the Met Office reported that the UK had already seen more days above 30°C than the whole of 1976, and 2026 became the first year on record to reach 35°C in May, June and July. Wales was running 2.7°C above its average maximum temperature by the halfway point of the season, and average minimum temperatures were tracking at record highs for the time of year, limiting the cooling that normally comes with nightfall.
Senedd Research reported that over 700 Welsh schools closed during the June heatwave. An assessment led by Imperial College London estimated around 128 heat-related deaths in Wales across May and June 2026, with roughly 42% of the wider England and Wales total attributed to the additional warming caused by human activity.
A measured trend, not a run of luck.
A single hot summer could be weather. The pattern behind it is not. Senedd Research found that the number of days exceeding heatwave temperature thresholds in Wales roughly doubled between the periods 1981 to 2000 and 2001 to 2020. That is not a projection or a model. It is a count of what has already happened, measured at weather stations across the country.
The peer-reviewed State of the UK Climate report, published in July 2026, confirmed that 2025 was the UK's warmest year on record. Wales was the second warmest on record, at a mean of 10.29°C, which is 0.88°C above the long-term 1991 to 2020 average. That distinction matters: 2025 broke the UK record, but not the Welsh one, and stating it accurately is part of why this page exists. The overall picture, though, is the same in Wales as it is across the rest of the UK. Every decade since the 1980s has been warmer than the one before it, and the warming is not distributed evenly across the year. Summers and early autumns are absorbing a disproportionate share of the increase.
The Met Office reported separately that the chance of exceeding 40°C somewhere in the UK is now over 20 times more likely than it was in the 1960s. The UK first crossed that threshold at Coningsby in Lincolnshire in July 2022, the same spell that produced the all-time Welsh record at Hawarden. Before that year, 40°C had never been recorded in Britain.
What the attribution science actually says.
Attribution studies ask a specific question: how much more likely did climate change make a particular event? Two are relevant here, neither of which studied Wales directly, and that caveat is worth stating clearly.
Researchers at World Weather Attribution found that human-caused climate change made the July 2022 UK heatwave at least 10 times more likely. That study covered a region bounded roughly by central England, from just north of London to the Midlands, and clips only the eastern edge of Wales. It is UK evidence, not Welsh evidence, and we are not going to pretend otherwise.
A second World Weather Attribution study, published in June 2025, found that the probability of a June heatwave in southeast England had increased by a factor of 9 compared with pre-industrial conditions. That study was limited to stations in Cambridgeshire, Hertfordshire and Surrey, and does not include Wales at all. What both studies share is a clear direction: the kind of heat events people experienced in those summers are far more likely now than they would have been without the warming that has already happened.
What the future projections look like.
Projections are probabilities, not predictions, and that distinction matters. The UKCP18 headline findings estimate that a summer as hot as 2018 now has a 12 to 25% chance of occurring in any given year, rising to around 50 to 60% by mid-century. Those figures describe a summer as hot as 2018 specifically, which was the UK's joint warmest at the time it was published. Summer 2026 was hotter than 2018, so a summer like this one is rarer than even those figures suggest.
Senedd Research projects a further 50% rise in the number of hot days in Wales at the level of global warming expected by 2050. Whether any individual summer breaks a record is not something a probability can tell you. What the numbers do say is that the summers we used to consider exceptional are becoming ordinary, and that the direction is not reversing.
Why Welsh housing makes it worse.
Rising outdoor temperatures are one problem. What happens inside an older Welsh house is another, and it is the one that turns an uncomfortable afternoon into a difficult night. Terraced houses built with heavy masonry, brick and slate were designed to hold warmth through a Welsh winter. They do that job well. The same thermal mass absorbs heat all day during a heatwave and releases it slowly through the evening, which means the indoor temperature can still be climbing at midnight while the air outside has already cooled.
This is not a niche problem. Terraced housing makes up a larger share of the Welsh housing stock than anywhere else in the United Kingdom. Many of those terraces are pre-1919 solid-wall construction, with no cavity to insulate and windows on the front and back only. Research carried out for the Climate Change Committee found that half of UK homes already suffer from overheating risk, and that smaller bedrooms and loft rooms are the worst affected, which describes the upstairs of a two-up-two-down almost exactly.
In a mid-terrace property with no side return and limited cross-ventilation, there is very little a window can do once the outdoor temperature drops below the indoor one, because the trapped heat has nowhere to go quickly enough. This is the practical reason that minimum overnight temperatures, the ones the Met Office reported tracking at record highs in 2026, matter more to a terraced house than the headline daytime peak. A house that reaches 32°C in the afternoon and drops to 22°C by midnight is manageable. A house that reaches 32°C and is still above 27°C at two in the morning is where people stop sleeping properly, and where the health effects of sustained indoor heat start to accumulate.
What we take from this.
We fit cooling into Welsh houses for a living, and this is why we take it seriously. Nothing on this page is a sales pitch, and nothing here predicts what next summer will do, because the science does not work that way and pretending it does would not be honest. What the evidence does say, measured by people whose job it is rather than stated by us, is that the climate Welsh houses were built for is not the one they are living through now, and that the gap is widening.
If you would like to know what that means in your own house, the health and sleep guide covers the indoor side of it. If you already know you want to do something about it, you can build a quote in about two minutes or book a free survey and we will come out and measure up properly. The coverage map shows whether you are in our patch.