Pea Soup

By December 1952, Londoners had been living with filthy air for so long that it had become part of the city’s identity.

Coal smoke had mixed with London’s natural fog for centuries. Complaints about the city’s smoky air can be traced back to the Middle Ages, and attempts to restrict coal burning had repeatedly failed. As London industrialized in the 18th and 19th centuries, the problem became dramatically worse. Factories multiplied, the population surged, and more than a million residents eventually relied on coal for heat. On certain cold, still days, smoke from thousands of chimneys mixed with moisture in the air and produced the thick yellow-brown fogs Londoners came to call “pea-soupers.”

They could be awful. An 1813 smog was reportedly so thick that people could not see across the street. In December 1873, another was followed by a death rate roughly 40% above normal. Similar spikes followed severe fogs in 1880, 1882, 1891, 1892 and 1948. By the early 20th century, London’s fog had become famous enough to appear in literature, paintings and postcards. What visitors found eerie, Londoners largely regarded as an unpleasant fact of life.

That familiarity mattered.

The winter of 1952 had turned bitterly cold by late November, and Londoners responded the way they always had: they put more coal on the fire. Home heating in the city still depended heavily on open coal fires, while factories and large coal-fired power stations added their own smoke. Diesel buses had recently begun replacing London’s electric trams, adding another source of pollution. There is also evidence that many homes were burning particularly dirty coal because Britain, still struggling economically after World War II, was exporting some of its higher-quality coal abroad.

None of those things, by themselves, was especially unusual. What changed was the weather.

On December 4, a large area of high pressure settled over southern England. Under ordinary conditions, smoke from London’s chimneys would rise and eventually disperse. But the high-pressure system created what meteorologists call a temperature inversion: cold air became trapped near the ground beneath a layer of warmer air above it. There was almost no wind to move the pollution away. Early on December 5, moisture condensed near the surface and formed a layer of fog perhaps 100 to 200 meters deep. Into that fog poured the smoke of millions of coal fires, factories and power stations. The atmosphere had effectively put a lid on London.

At first, there was little reason for alarm. Friday morning was foggy, certainly, but London was often foggy. People went to work. Children went to school. Shops opened. Then the fog began to thicken.

By nightfall, visibility in parts of the city had fallen to only a few feet. Pedestrians who knew their neighborhoods intimately became disoriented because they could no longer see curbs, intersections or landmarks. Faces and clothing became streaked with soot. The air smelled of coal smoke and, in places, sulfur. Drivers abandoned cars in the roadway when they could no longer see where they were going. Police officers stood at intersections holding flares, while some bus conductors got out and walked in front of their buses with flashlights, guiding drivers who could scarcely see beyond the windshield.

The trains had their own solution. Engineers moving slowly through the darkness could not reliably see signals, so small explosive charges were placed on the rails. When a locomotive rolled over one, the bang warned the driver that a signal was ahead. Flights were canceled. Boats stopped moving on the Thames. Eventually much of the bus system shut down as well. The Underground, protected beneath the streets, became one of the few reliable ways to move around the city.

And going indoors didn't necessarily solve the problem.

The smog crept through cracks beneath doors and around windows. It entered cinemas and theaters. At Sadler’s Wells, a performance of La Traviata had to be abandoned because the smog had worked its way into the auditorium and obscured the stage. At the Smithfield livestock show at Earl’s Court, young cattle began struggling to breathe. One died, and several others were slaughtered to prevent them from suffocating.

Meanwhile, Londoners were getting sick.

Hospitals saw growing numbers of people suffering from respiratory problems, especially the elderly and those with existing heart or lung disease. Yet there was no single dramatic moment when the city understood that it was in the middle of a mass-casualty event. People weren't fleeing an approaching fire or watching floodwaters rise. They were breathing air that looked like air Londoners had breathed before, only thicker.

The smog remained through Saturday, Sunday and Monday. Each day London’s chimneys continued putting pollution into an atmosphere that still had nowhere to send it. The Met Office estimates that during each day of the event roughly 1,000 tons of smoke particles and hundreds of tons of sulfur dioxide were released beneath the inversion, with much of that sulfur dioxide ultimately converted into sulfuric acid.

Then, on Tuesday, December 9, the weather changed. Wind finally arrived and the poisonous cloud began to break apart. London slowly reappeared beneath it, coated in greasy black soot.

Only afterward did the scale of the disaster become clear. About 4,000 excess deaths were initially attributed to those five days. Later research, looking at the elevated mortality that continued afterward, estimated that the true toll may have been closer to 12,000. Parliament eventually responded with the Clean Air Act of 1956, beginning the long process of moving London away from the coal smoke that generations had accepted as part of living there.

What I find fascinating is that almost nothing responsible for the disaster was new.

London didn't suddenly discover coal on December 5. Its homes had burned it for generations. The factories were already there. So were the power stations. Fog certainly wasn't new. Even deadly fog wasn't new.

For years, London had experienced essentially the same ingredients without anything remotely approaching December 1952. And that probably made each ingredient feel a little safer than it really was.

There is a version of that phenomenon in our financial lives, too. We can carry a large position in one company for years without trouble. We can allow spending to rise until there isn't much margin between what comes in and what goes out. We can postpone an estate document, an insurance review or some other piece of financial housekeeping because there has never yet been a day when we desperately needed it. A retiree can live through years of cooperative markets and gradually become accustomed to the idea that markets will cooperate.

Nothing necessarily goes wrong tomorrow. In fact, nothing may go wrong for a very long time. That is what makes these situations so easy to become comfortable with.

We tend to think experience teaches us about risk, and usually it does. But sometimes experience teaches us the wrong thing. Ten uneventful years can mean a situation is safe. Or it can simply mean the particular conditions required to expose the risk haven't lined up yet.

London had coal. London had smoke. London had fog. It had lived through all three countless times.

Then, for five days in December 1952, the temperature fell, the fires burned harder, the wind stopped blowing, and the air above the city refused to move.

The ingredients had been there all along.

What changed was that, this time, they all arrived together.