The Great Smog of London woke the world to the dangers of coal

For five days in December 1952, a thick fog strangled the streets of London—a disaster that killed thousands of people and opened the door to landmark environmental protections.

Donald Acheson knew London like the back of his hand. But while working a shift at a hospital in the bustling city center in December 1952, a routine errand turned into a disorienting—and dangerous—brush with disaster.

An ominous fog had been filling the city, enveloping it in a dense layer of black, sooty air. Lost on streets he knew well, the young doctor had to “creep on the pavement along the walls of the buildings, to the next corner, to read the name of the street.” He made his way back to the hospital amid what he later remembered as “eerie silence.”

The smog was inside the hospital where Acheson worked—and inside the lungs of his emergency-room patients. Soon, the hospital reached a breaking point, its morgue overflowing with patients who had died of respiratory and cardiac problems.

(What is air pollution? Here are the basics.)

The terrible, choking fog had a nickname—the Great Smog. Between December 5 and 9, 1952, the environmental disaster strangled London. It would affect British health—and its climate—for years to come. Here’s how the fog struck the chilly city and how it still affects the United Kingdom today.

Consumed by coal

London had long struggled with its air quality, from the “Great Stink” that wafted off the Thames’ sewage-polluted waters in the 1850s to the city’s epic “pea soupers”—long periods when emissions from factories and heating stoves suspended a greenish fog above the streets. In 1905, doctor Harold Antoine des Voeux coined the term “smog,” combining “smoke” and “fog,” to describe the city’s air.

At the time, Britain was a titan in coal production. The industry peaked in 1913, when the nation produced a full quarter of the world’s total coal—a staggering 292 million tons. Though the nation turned to oil along with the rest of the world during the First and Second World Wars, the British coal industry survived in part because Britons still used coal to heat their homes.

(What you need to know about coal and other fossil fuels.)

As art historian Lynda Nead explains, the idea of an open coal hearth at home had “almost folkloric associations,” especially during and after the chaos of World War II, which created a major housing shortage in Britain. Crowded Londoners saw hearth and home as more important than ever in the war’s aftermath; in 1942, Nead writes, one survey found that 78 percent of Britons used coal.

As the United Kingdom reconstructed after the war, the country debated whether and how to “keep the home fires burning.” But home coal usage remained largely unregulated.

How the smog started

As Londoners stoked their fireplaces to combat a cold winter in December 1952, a weather pattern emerged that would turn their coal smoke into a deadly fog.

On the evening of December 5, with temperatures hovering at about 32 degrees, the heat and smoke of the coal fires rose into the atmosphere like always. On a typical winter day, they would rise and cool in the chilly atmosphere before wafting away.

Instead, the opposite occurred thanks to a high-pressure weather system known as an anticyclone. A blanket of warm, moist air stalled over London, pushing the air toward the ground. There, the cold temperatures condensed the water vapor in the air into fog. Known as a temperature inversion, the weather phenomenon trapped the fires’ emissions over the city.

According to the British Meteorological Office, the fog was up to 200 meters thick, and with each passing, chilly day, the city’s polluters emitted up to a thousand tons of smoke and 2,000 tons of carbon dioxide per day. Meanwhile, sulfur dioxide, a colorless gas created when coal burns, became trapped in the atmosphere. There, it mixed with the water particles of the fog and became sulfuric acid, enveloping the city in a haze that was, in essence, made up of acid rain.

Health emergency

Chaos resulted as the fog blackened. With visibility at near zero, drivers could not safely traverse roadways and the city shut down its public transportation system. People on the city sidewalks couldn’t see as far as their own feet. Inside was little better; one correspondent for the Guardian wrote that “greasy grime” covered indoor surfaces and obscured movie screens.

As the weekend progressed, so did the health effects of the smog. Hospitalizations increased 48 percent that week, and respiratory hospital admissions more than doubled. The stagnant smog was choking the city.

Assuming the event was just another “pea-souper,” the nation’s Conservative government was slow to respond to the Great Smog and public health authorities downplayed the effects of the polluted air. Prime Minister Winston Churchill never commented publicly on the event or its aftermath.

But the December smog was unlike anything London had ever seen. By the time it lifted four days later, the deaths had already begun. Though florists quickly ran out of flowers and funeral homes exhausted their supplies of caskets. That week, the government tallied 3,000 death—but the reality was much more dire.

(Subscriber exclusive: See how polluted air attacks our bodies.)

In 2012, researchers analyzed historic sources to determine the Great Smog’s true death toll—finding that it caused about 12,000 more deaths than would otherwise have occurred. And the effects far outlasted the smog itself. Children exposed to the smog during their first year of life were nearly 20 percent more likely to develop asthma during childhood and 9.5 percent more likely to develop it as adults; in utero exposure meant a nearly 8 percent increase in childhood asthma.

Environmental legacy

The Great Smog’s effects live on in another form—that of environmental regulations. Though the British population had been largely complacent about coal smoke for decades, public opinion began to turn. After dragging its feet initially, the British government finally declared clean air a legislative priority.

The Great Smog drove British lawmakers to pass the world’s first comprehensive national air pollution law in 1956. The Clean Air Act outlawed the emission of “smoke nuisances” or “dark smoke” and required new furnaces to emit little or no smoke. In 1968, lawmakers further strengthened the laws. It would take the rest of the world years to follow suit; the United States passed its own Clean Air Act in 1970, a full 14 years after the Great Smog.

(The U.S. Clean Air Act has saved millions of lives and trillions of dollars.)

By then, the smoke had lifted over most of England. Political scientist Howard A. Scarrow explains that smoke emissions nationwide declined 38 percent in the decade between 1956 and 1966, with concentrations of coal-produced smoke falling 76 percent in London alone. Thanks to its landmark air pollution legislation, the city hasn’t had a “pea-souper” since the 1960s.

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