Historically, very few UK homes have had any sort of air conditioning – neither the country’s climate nor its culture have called for it. But things are changing. Global heating is no longer a distant threat but a felt reality, air pollution is taking people’s lives, and our cities are getting so noisy they’re causing elevated blood pressure and heart problems. All these things make home air conditioning more attractive than opening a window. In summer 2020, sales of domestic cooling systems were 20% up on summer 2019, with home working understood to be the major driver. Sales have been up in recent years in Europe as well. The continuing Covid-19 pandemic has changed working patterns, and those used to working in cooled offices are often at home struggling to concentrate or worse, to control heat-related aggression. So if you have a couple of hundred quid, and work from home in the armpit of an A-road and the “London Thunderground”, you may well conclude that splashing out on a portable AC unit is the way to go. But is that really the best we can do? Because while it might be nice for those lucky enough to enjoy the delicious cool air, AC actually makes things worse for everyone else. There are a variety of AC units available, and some will be more efficient than others, but the best-case scenario is they’re electric, and until our electricity grid is 100% renewable, all energy use is exacerbating climate change. Most units will be ejecting hot air into the urban spaces between the buildings, so you are heating up the outdoors and increasing discomfort for anyone in the line of your hot exhaust, including people outside and people desperately trying to get some fresh air in through their windows. Almost all systems use refrigerants that are extremely potent greenhouse gases. Also, as with all electrical equipment, AC units include rare Earth metals that leave a wake of devastating social and ecological harm through their extraction and processing. There are other, well-established solutions we can turn to. If you can, retrofit your home to make it more comfortable year-round with loft insulation (it works both ways!), external shading (such as shutters), painting external walls and flat roofs in pale colours that reflect the sun’s energy back out, and planting deciduous trees in front of south-facing windows that provide free shading in the summer that conveniently disappears in winter. Quicker fixes include closing windows when it’s hotter outside than inside to trap more cool air, closing blinds and curtains or fashioning external shades, and reducing heat by turning everything off standby. For new-build homes or deep retrofits, we need to apply principles of passive design such as treating facades differently depending on whether they face north, east, south or west, introducing overhangs, especially on south-facing facades, positioning windows and organising layouts to allow cross-flow ventilation, and of course, external shutters. In the UK we’ve not typically built our homes with shutters since glass became the preferred material for holes in walls, but maybe it’s time they made a comeback. Wouldn’t towns and cities resplendent with beautiful, colourful, shutters be preferable to a melted wasteland with a few fortresses decorated with condenser units? There is of course a place for air conditioning in our built environment, especially in care settings. But the solution is definitely not a glut of individual, inefficient AC units. Rather the solutions must be large-scale and infrastructural, such as heat pumps connected to fifth-generation heat networks – a recent pilot in Plymouth allowed users to both import and export heat into the network, improving efficiency and sharing of resources. Fundamentally, this comes down to short-term individual solutions versus longer-term collective action. How can we culturally adapt to our new climate? How can employers offer more flexibility? How can the construction industry (including AC manufacturers and installers) be encouraged to maximise passive – non-power-sucking or chemical-burning – measures before relying on active cooling? How can the government offer good advice, resources and grants to retrofit all our homes for long-term sustainability? How can we learn from indigenous technologies that better incorporate collective management of resources and collaborate with natural systems? For example, the subak irrigation system in Bali, which collectively manages steep terraces of rice paddies with a network of channels that distribute cooling water while facilitating healthy nutrient cycling and organic pest control. One possible future scenario is that those who can afford to will use more and more energy and puff out more and more emissions, keeping themselves comfortable in an increasingly hostile climate, making it more and more inhospitable for everyone else. As the heatwaves roll in, is this the path we want to set ourselves on? Smith Mordak is director of sustainability and physics at engineering consultancy Buro Happold