If you’ve felt uncomfortably hot in a city this summer, c

If you’ve felt uncomfortably hot in a city this summer, chances are it’s not just because of the weather. Look around any urban centre and you’ll see the built environment itself exacerbates summer temperatures.

Vehicles stuck in traffic emitting heat. Airconditioners pumping waste heat into the air. Concrete and asphalt across almost every surface, absorbing and radiating the sun’s rays. Urban canyons formed between tall buildings, trapping heat at the street level.

All these factors contribute towards a phenomenon called the “urban heat island” effect, which results in cities being up to 10C hotter than the surrounding countryside. How do we to tackle this?

A typical response on a hot day might be to turn up the aircon. But this fuels a vicious circle of heating the outdoors to cool the indoors, making external spaces more uncomfortable still, and at a significant cost. Airconditioning currently accounts for around one-fifth of building-related global electricity usage, or 2.5 timesthe total electricity use in Africa.