At first sight, the view could be mistaken for the rolling hummocks of Hobbiton, right down to the perfectly circular doors opening out of the lush green hillside. But the doors are made of glass, and inside them are not cosy hobbit holes but an array of large mechanical steel arms and levers holding some of the doors ajar.

These hills are part of the roof of the California Academy of Sciences in San Francisco, US. The undulating green roof is one of a series of engineering and design features that make the academy one of the largest passively ventilated spaces in the US. This means that even in the peak of summer, the bulk of this building relies on clever manipulation of the elements to stay cool, with next to no air conditioning.

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Roofs like these are one way that architects, engineers and designers are rethinking buildings to find ways to keep them cool without air conditioning. The challenge is becoming increasingly urgent; it has been yet another scorching year, with heatwaves steamrolling Australia, southern Asia, North America and Europe. To deal with heatwaves, made more frequent by climate change, the number of AC units is expected to more than triple worldwide by 2050. As well as guzzling huge amounts of electricity, AC units contain refrigerants that are potent greenhouse gases. These refrigerants are in fact the fastest-growing source of greenhouse gas emissions in every country on Earth.