July 20, 2022 1:50 PM EDT

Temperatures in the U.K. surpassed records on Tuesday, as an Europe-wide heat wave pushed the mercury up to 104.5°F (40.3°C). The unprecedented weather caused major disruptions in a country whose infrastructure was designed for a damp, mild climate—train services were delayed amid fears of buckling tracks, while London Luton airport closed a runway after heat melted the tarmac.

On a more individual level, many Brits were left sweltering without any relief for one simple fact: less than 5% of homes in the U.K. have air-conditioning. It’s a sharp contrast to the U.S., where the figure hovers above a whopping 90%. The lack of air-conditioning in the U.K. even prompted some to improvise, with videos of make-shift units circulating on social media.

There are several reasons why few Brits have air-conditioning—the most obvious being the country’s relatively mild weather. Average summer temperatures range between 55°F (13°C) and 75°F (24°C), and winters can last up to five months. British infrastructure has been designed with a greater emphasis on heating given these cooler temperatures. But as the climate crisis makes heat waves longer and more frequent, the need to focus on cooling is becoming ever more apparent.

Read more: 5 Ways the U.K. Is Not Built for Extreme Heat

Another key difference between the U.K. and the U.S., explains Smith Mordak, sustainability director at engineering consultancy Buro Happold, is the nature of the two countries’ housing stock. According to U.K. government figures, one in six homes in England date from before 1900, while 46% were built between 1930 and 1982. “[Air-conditioning] technology either wasn’t available or widespread then,” says Mordak, so most homes weren’t built to accommodate them. The median age of U.S. homes is around 40 years old, and air-conditioning became standard for new properties from the late 1960s onwards.

While it’s possible to retrofit older houses with air-conditioning units, many are built with brick and have no—or very small—air cavities. This makes it harder and more expensive to install air-conditioning, particularly when pre-existing hot water and electrical systems get in the way. It’s also common in the U.K. to live in what Brits call a “terraced” house—known as a row house in the U.S.—a property that shares a wall with the neighbors next door. These terraced homes limit the options of where to install the condenser, the outdoor portion of air-conditioning units.

The way Brits heat their homes is another obstacle to installing air-conditioning. “British housing is heated primarily through water-based radiators, or ‘wet heat,’ and a smaller proportion of electric heating,” says Ian Hamilton, a professor at University College London’s Energy Institute. By contrast, the majority of homes in the U.S. are heated with “dry heat,” a warm air system using a gas- or oil-fired furnace. When it comes to installing an air-conditioning unit, Hamilton says, it’s “much more straightforward” to add to a dry heat system than a wet heat system. This is because “you maintain the way you distribute the heat or cooling effect—via the air—while switching between a furnace or A/C unit.”

While it’s rare to have air-conditioning in U.K. homes, it’s more common at work. It’s hard to determine exactly how prevalent air-conditioning is in offices, but a 2012 study by the Building Research Establishment estimated that 65% of office spaces and 30% of retail space in the U.K. have air-conditioning. Office buildings tend to have been built more recently than many British homes, and companies have more money to spend on retrofitting older buildings.

But both the shift to remote working and the disruption to public transport caused by the heat meant that many British employees had to work in their homes on Monday and Tuesday without air-conditioning.

Despite periodic spikes in sales of air-conditioning units, Hamilton predicts that they will only become widespread in the U.K. when summer heat waves become more frequent and last longer. But climate change is pushing the world in this direction—a recent study shows that Europe is a heat wave hotspot, with temperature extremes increasing three to four times faster than regions on similar latitudes, partly due to changes in the jet stream—air currents five to seven miles above Earth’s surface.

Read more: Summers Are Becoming Unbearably Hot Before They Even Start

Ultimately, experts tell TIME that more air-conditioning units in the U.K. isn’t the answer to extreme heat. Air-conditioning systems pump out carbon emissions that contribute to climate change, while the production of new units requires the environmentally destructive extraction of rare metals. To achieve its target of net zero, the U.K. government should, according to Mordak, be reconfiguring buildings and cities to promote “passive” methods of cooling—insulation, shading and tree planting—rather than energy-guzzling cooling systems.

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