This weekend, north-eastern Spain will be nearly halfway to the boiling point of water. “Hell is coming,” the TV meteorologist Silvia Laplana tweeted after the weather service forecast temperatures of 42C and warned of forest fires. In Paris, temporary swimming pools will be constructed on housing estates, water distributed free to the homeless, and parks opened all night. Oppressive heat forces us to wonder: if this is now, what will then be like?

The human body begins to shut down in 41C heat. At 50C, our cells start to deteriorate and the risk of organ failure sets in. Asphalt melts and the soles of shoes soften on pavements. Heat is intensified in cities: concrete, brick and dark surfaces absorb heat during the day and emit warmth at night. While the wealthy can escape in air-conditioned apartments and office blocks, those who don’t have AC, including the homeless and urban poor, will struggle to survive the heat. As the planet warms up, a new form of inequality will emerge between those who can afford to stay cool, and those who are condemned to remain hot.

Not long ago, heat in excess of 40C was considered anomalous, but such temperatures are fast becoming normal. At present, about 30 per cent of the world’s population is exposed to uninhabitable temperatures for at least 20 days a year. By 2100, this is projected to grow to 74 per cent. The World Health Organisation estimates that heatwaves could kill around 255,000 people each year by 2050. In the UK alone, the number of future heat-related deaths is projected to increase by 257 per cent.

Humans have long used technology to control their environment. During a recent visit to Connecticut, I was reminded of this sensation. Though it was sweltering June weather outside, we wore layers. Driving in an air conditioned vehicle to an air conditioned stripmall, I became newly aware of the clean stream of frozen air and its peculiar form of sensory deprivation. Air conditioning has created new types of social space. Stepping from one cooled space into another, I reflected that some people probably spend their lives like this, forever escaping the outdoors in their own hermetically sealed map of climate-controlled cars, homes, offices and supermarkets.

Perhaps more than any other invention, air conditioning has changed how we experience space. It powers office blocks, shopping malls and gyms. It makes storing medical supplies and computer servers possible. It has allowed humans to tame previously uninhabitable regions: the glass and steel skyscrapers of the Gulf states would be impossible without AC. The US sunbelt, where air conditioning was pivotal to the expansion of suburban sprawl, reflects the same phenomenon.

Clunky air conditioning boxes are a ubiquitous sight in the US, retrofitted to the windows of period houses and stacked on the side of multi-story conurbations. They’re rarely seen in the UK. “Britain’s temperate climate has left it with terrible buildings – there’s no culture of high-performance architecture that resists cold or heat, of the type you see in, say, Scandinavia or Malaysia,” Phineas Harper, deputy director of the Architecture Foundation tells me over the phone. The National Grid believes this will change in the future. A report from the utility company forecasts a 2.8C increase in the UK’s temperature by 2050 is a 50:50 probability, which would make the UK as warm as Turkey. It predicts a substantial increase in the number of air conditioners in the UK – from 0.3 million units today, to around 20 million in 2050.

Yet in a cruel irony of climate change, cooling the planet down can actually make it warmer. Toby Peters, a professor at the University of Birmingham’s Energy Institute, describes the “heat island” effect to me, where human activity makes some parts of the city significantly warmer than others. The first heat island measurement in London in 1999 showed that night-time temperatures around the British Museum in August were up to 9C higher than in Heathrow. Air conditioning amplifies this reality. In Phoenix, Arizona, ambient heat expelled from AC machines warms the surrounding environment by almost two degrees. For inhabitants living in the top floor of a block of flats, AC machines will mainly exhaust heat created by humans below.

Air conditioning, like car ownership, is the perfect emblem of capitalist individualism. It buys comfort and convenience while polluting and heating the surrounding environment. The US consumes more energy for air conditioning than the rest of the world combined. In China, owning an AC machine signals that one belongs to the increasingly affluent middle class – the country bought fifty million new domestic AC units in 2010 alone. The result of air conditioning is doubly polluting: global use of air conditioning accounted for 1,932 terawatt-hours of electricity in 2018, and emits potent hydrofluorocarbon gases into the atmosphere.

Controlling the temperature of our environment is one of the greatest challenges we face. “There are a lot of lessons we can learn from countries that have been hot for millennia”, Harper tells me. Architecture that makes clever use of shading, water and natural ventilation can avoid some of the need for mechanical cooling. Public courtyards built around a central fountain, for example, allow moisture to permeate the air and create spaces of cool and shade.

Contemporary architects like Diébédo Francis Kéré design spaces that vastly reduce the need for AC – Kéré’s Gando Primary School in Burkina Faso has an elevated roof and perforated clay ceiling to keep classrooms cool. In rural India, researchers are working on a communitarian alternative to individually owned AC units that groups together services dependent on the cold, like vaccines, medicine and food. A thermal network of “district cooling” in Paris, meanwhile, is more efficient than individual AC units, and takes the heat out of the urban environment rather than just displacing it.

“Because it costs money [and] is no longer free, conditioned space inevitably becomes conditional space,” writes the Dutch architect Rem Koolhaas. Entry to air-conditioned shopping centres, gymnasiums, cinemas and supermarkets hinges on disposable income. As cities prepare for climate change, they have a choice: finding solutions that share the cold, or becoming more like Dubai – a place where the rich escape the heat in air-conditioned malls while the urban poor swelter in the sun outside. Air conditioning, in other words, deepens existing forms of social exclusion. In the cities of the future, the rich may wall themselves into privately owned refrigerators, while those without air conditioning sweat for want of shade.