Our cities are sweltering. And they've been designed to cook us. According to climate estimates, the extreme temperatures registered in recent heatwaves in the UK will, by 2040, constitute normal summer temperatures. Heatwaves will become longer and more intense and our cities, constructed from a mix of high density materials with high thermal conductivity, will get hotter and hotter.
The urban heat island effect is not a new phenomena, but countries like the UK are more exposed to the threats of extreme heat as summers get longer and hotter. Take London as an example. Temperatures in the UK's capital are, on average, one to three degrees celsius hotter than the surrounding countryside.
Unlike more southerly cities on the European continent, which have been better-designed to cope with higher temperatures, London is woefully ill-prepared for a warming world. And that's really bad news for your hot and sweaty office. Simply put: London wasn't built to be this hot, and cooling it down is going to take a lot of time and money.
First, the science of why cities get so hot. In rural areas the ground is less dense and has a lower heat capacity. Trees provide an insulating layer above ground, blocking out the extreme heat of the sun. And, at night, rural areas cool down as most of the heat stored up during the day escapes.
In urban areas, roads, pavements, glass and concrete buildings, cars and people combine to heat up the air in a vicious cycle. When exposed to the sun during the day, the high density surfaces of a city become very hot. With nowhere to go, this rapidly heats up the air around it. And at night, blocked in by high density materials, the heat struggles to escape.
Row upon row of tall buildings also block out any breeze, with the roofs of these buildings often covered in dark, artificial materials that trap more heat. All that hard concrete and asphalt is, by design, also terrible at storing moisture. On a hot day, moisture in natural ground is released into the air to cool it down (a bit like when you sweat). In the concrete jungle of a city, all that rain runs down into drains. That's great to stop a city from flooding, but not so great when you're in the midst of a heatwave.
Right now, your London office might not be air conditioned. Soon, your employer will likely have little choice. But adding air-con to London's growing urban heat island predicament will only make things worse. Air-con drives climate change by increasing electricity demand which is mostly met by burning fossil fuels. This, in turn, makes it hotter, which then requires more air-con units. It's expensive, it's dirty and it's a woefully short-term solution. Sure, air-con could and should be powered more by renewable energy (especially solar) but that will only help so much. It might cool your office down, but the curse of air-con is that it heats cities up.
So what can be done? Simply, cities like London need to go green. And fast. Buildings need better insulation, cars need to be taken off the roads and electric vehicle use needs to increase. The city needs more parks, more trees, more grass. And it needs all of this not just in isolated urban oases but on walls and on roofs and on busy city centre streets. Every surface has potential.
But some of the solutions are more simple. Starting right now, we should paint more things white. Surface albedo, essentially a measure of how well a body reflects solar radiation, is far higher on lighter-coloured surfaces. Think of your typical picture-postcard Mediterranean town. Now think of your typical London street.
But London, and other more temperate cities that are likely to experience longer, hotter summers, are not an exact comparison with their warmer Mediterranean counterparts. Designing solutions to London's urban heat island problem need to take into account that, for most of the year, the city needs heating up. Helpfully, environmental simulations have shown that it is more important to reduce the requirement for cooling a city like London than to reduce the requirement for heating it. Simply put: making it easier to cool London down will have a far larger positive environmental impact than making it easier to heat London up.
Major new developments in London are already taking this into account. Buildings are being oriented to minimise the amount of heat entering them during in the summer. Passive and mechanical ventilation systems – including those that efficiently cool buildings during the night – will also reduce the urban heat island effect the need for air-con.
Failure to respond properly could have a dire impact on the economy of London and the health of its inhabitants. Ultimately, urban heat islands cost money. The heatwave that hit Europe in the summer of 2003 — the hottest summer on record — claimed more than 70,000 lives. In the UK alone, around 2,000 people died in the space of ten dangerously hot days during August 2003. We already know how we can redesign and rethink cities like London to cope better with the crippling urban heat island effect – now we need to take decisive action.
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This article was originally published by WIRED UK
