An extraordinary investigation into shade, bringing together science, history, urban design, and social justice to change the way we think about a critical natural resource that should be available to all.

On a 90-degree day in Los Angeles, bus riders across the city line up behind the shadows cast by street signs and telephone poles, looking for a little relief from the sun’s glaring heat. Every summer such scenes play out in cities across the United States, and as Sam Bloch argues, we ignore the benefits of shade at our own peril. Heatwaves are now the country’s deadliest natural disasters with victims concentrated in poorer, less shady areas. Public health, mental health, and crime statistics are worse in neighborhoods without it. For some, finding shade is a matter of life and death.

Shade was once a staple of human civilization. In Mesopotamia and Northern Africa, cities were built densely so that courtyards and public passageways were in shadow in the heat of the day, with cool breezes flowing freely. The Greeks famously philosophized in shady agoras. Even today, in Spain’s sunny Seville, political careers are imperiled when leaders fail to put out the public shades that hang above sidewalks in time for summer heat.

So what happened in the U.S.? The arrival of air conditioning and the dominance of cars took away the impetus to enshrine shade into our rapidly growing cities. Though a few heroic planners, engineers, and architects developed shady designs for efficiency and comfort, the removal of shade trees in favor of wider roads and underinvestment in public spaces created a society where citizens retreat to their own cooled spaces, if they can—increasingly taxing the energy grid—or face dangerous heat outdoors.