Feeling the Heat? Blame Concrete

If your city was slammed by record-shattering heat this summer, you can partly blame the stuff the city itself is made of. The scorching temperatures across Europe and the U.S. in July were made worse by one of humanity’s most widely used but least-loved inventions: concrete.

To most people, concrete is just the ugly stuff used to pave paradise and put up a parking lot. But concrete is an invention as transformative to humanity as fire or electricity. Since it came into widespread use around the turn of the 20th century, this man-made stone has changed where and how billions of people live, work and move around.

Concrete gives us the power to dam enormous rivers, erect buildings of Olympian height, and travel from place to place with an ease that would astonish our ancestors. Concrete hospitals and schools can be built and repaired far more quickly than their counterparts of adobe, wood, or steel. Concrete roads help farmers get their crops to market, students to get to school, and sick people to get to hospitals in all weathers.

It’s an almost supernaturally cheap, easy way to quickly create sturdy housing for huge numbers of people. Concrete is strong, capable of holding thousands of tons worth of people, furniture, and water. It won’t burn or get infested with termites. And it’s incredibly easy to use. A single person can mix a batch of basic concrete and slap together a serviceable shelter. A well-financed contractor can pour the foundation of a towering building in a matter of days. Small wonder that it has become the skeleton of our cities—the primary material of almost every apartment block, shopping mall, and office tower, and of most of the roads connecting them. An estimated 70% of the world’s population now lives in structures made at least partly out of concrete.

For all its blessings, however, concrete incurs serious costs to people and the planet—including boosting the potency of heat waves.

If you’ve ever walked barefoot across a sunbaked parking lot, you know firsthand how concrete soaks up and retains the sun’s heat. When temperatures rise, the countless miles of concrete streets, sidewalks, walls and roofs in cities magnify that effect, creating a phenomenon known as urban heat islands. When combined with the heat released by vehicle engines, paved areas can boost the temperature in cities by as much as 22°F, according to the Environmental Protection Agency.

Soaring city temperatures aren’t just unpleasant. They can be lethal. Heat already kills more Americans than hurricanes, lightning, tornadoes, floods, and earthquakes combined. The urban heat island effect is ever more worrisome because more and more people are moving into cities. Over 81% of all Americans already live in urban areas. In developing countries from China to Nigeria, millions are leaving the countryside every year for a shot at a better life in cities . The number of urban dwellers worldwide is rising by as much as 78 million people annually, according to the United Nations Population Division. That’s the equivalent of adding nine New York Cities to the planet every single year.

Concrete production worsens the problem, too. The cement industry produces somewhere between 5-10% of all carbon-dioxide emissions worldwide, making it the third-largest source of global-warming, behind only coal-fueled power plants and combustion-engine vehicles.

Concrete is essentially just sand and gravel glued together with cement. To feed the construction industry’s needs, tens of billions of tons of sand are dug out of the earth each year, enough to blanket the entire state of California. Much of it is dredged from river beds, lake bottoms, and beaches. The process often slaughters river-dwelling fish and birds, damages coral reefs, undermines bridges and causes riverbanks to collapse.

There is so much money to be made off of sand that in some countries, organized criminal gangs have moved into the business. In India, Mexico, Kenya, Vietnam and elsewhere, hundreds of people have been beaten, tortured and murdered in recent years over sand.

The most frightening aspect of our dependence on concrete might be that the structures we build with it won’t last. The vast majority of them will need to be replaced—and soon, within decades.

We tend to think of concrete as permanent as the stone it mimics. It’s not. Concrete fails and fractures in dozens of ways. Heat, cold, chemicals, salt, and moisture all attack that seemingly solid artificial stone, working to weaken and shatter it from within. If it’s not monitored and maintained, most concrete slowly disintegrates. It’s especially vulnerable if it was made shoddily in the first place by builders looking to save a few bucks by using low-quality sand or skimping on steel reinforcement rods.

Many of the world’s concrete structures are already crumbling. The American Society of Civil Engineers says one-fifth of U.S. highways and one-third of the country’s urban roads are in “poor” condition. According to the Federal Highway Administration, nearly one-quarter of all the United States’ bridges are structurally deficient or functionally obsolete. America’s dams are in similarly dismal shape.

Worldwide, as much as 100 billion tons of poorly manufactured concrete structures—buildings, roads, bridges, dams, everything—may need to be replaced in the coming decades, at a collective cost of trillions of dollars.

We can’t stop using concrete completely; it’s far too useful as a building material. But in a rapidly warming world, we need to start thinking about its true costs.

Vince Beiser is author of The World in a Grain: The Story of Sand and How It Transformed Civilization, which was released in paperback on August 6.