2020 has been a year to forget.

Every time we turned around, a new threat. COVID. Tiger King. Murder hornets. It was always something else to kill our mind, body, or soul.

But I guess it could have been worse. At least the air wasn’t trying to kill us.

On December 4, 1952, a cloud began to descend over London. But even in a city reknown for its fog, this one was different. This one was killer.

A period of unusually cold weather had plagued the country for several days. This forced Londoners to burn more coal in an attempt to keep warm, filling the sky with black smoke. But this in and of itself wasn’t unusual. London had been burning coal for years; it was a plentiful resource, cheap and easily converted to energy. The city’s streets and buildings were black with residue. Citizens were used to the soot, grime, and fumes.

But since the end of World War II, Great Britain had found itself in debt. In order to pay for repairs, as well as reimburse allies for supplies and services, it had realized the value of its coal reserves and began to export them in earnest, leaving only the “scrapings” behind for its own citizens. The coal being burned in the homes and businesses of London that fateful December was of the lowest quality, containing a higher percentage of sulphur dioxide, which–when burned–resulted in a haze of sulphuric acid.

However, even this–as alarming as it sounded–was nothing to panic about. Breezes sweeping in from the coast would clear out the smoke before any lasting harm could be done.

Until they didn’t.

In early December, a weather pattern known as an “anticyclone” settled in over Great Britain. In this phenomenon, winds circle around a large area of high pressure, causing cold, stagnant air to become trapped beneath a dome of warm air, resulting in fog. Inside that dome, there is no moving air. No breeze, no breath of fresh air. It’s was if a giant lid had been placed over the city of London, trapping its inhabitants under a blanket of fog and smoke.

And, this time, it was poisonous smoke.

Naturally occurring fog mixed with a haze of airborne pollutants, creating a yellow-black “smog” that shuttered the city for five days. Visibility was reduced to only a few feet, making driving impossible and even walking dangerous. Public transportation–save for the Underground–was shut down; even ambulances were unable to make their necessary trips across the city. The smog seeped indoors, clouding people’s houses, closing stores, and cancelling movies, plays, and sporting events.

However, stalwart Londoners didn’t panic. They were used to fog. This was a bad one, yes, but it was more of a nuisance than a catastrophe. They did their best to go about their business, waiting for the irritation to blow over, most of them unaware of the mess slowly beginning to accumulate inside city hospitals.

Unlike normal London fogs, this time more and more people were seeking medical help for breathing issues. Surprised doctors were overwhelmed with afflictions of the respiratory tract. Even more alarming were the instances of hypoxia or, in the most dreadful cases, patients choking to death on pus from infections inside their lungs.

The “Great Smog of London” lasted for five days, but it was only after its abatement that the true nature of the disaster was understood. An investigation of medical records revealed that over 100,000 people were made ill by the pollutants, and at least 4,000 died, although subsequent research puts that number much higher. Some experts claim the fog may have taken upward of 12,000 lives.

For the first time, scientists began to truly understand the danger posed by airborne pollutants. In 1956, the UK passed the Clean Air Act, which mandated movement toward smokeless fuels and required reduced emissions of gases, grit, and dust from chimneys and smoke stacks. Progress was slow moving–you can’t undo a hundred years of energy-harnessing overnight–but it was still progress. When another smog event descended on the city in 1962, 750 people died, a tragic number but a sure sign of London’s slow march in the right direction. Reducing air pollution remains, even all these years later, a frustratingly gradual process but it takes only a glance back seventy years to see how far we’ve come.

So, when you lay down tonight, annoyed and perhaps a bit fearful about what 2020 has done and what it may still have up its sleeve in its last few weeks, let’s just remember that at least we don’t have deadly fog to deal with anymore.

Do we?