Air conditioning: our plague-helper

The Black Death killed 75 to 200 million people in Eurasia, peaking in Europe from 1347 to 1351. It is estimated to have killed 30% to 60% of Europe's population. In total, the plague may have reduced the world population from an estimated 475 million to 350–375 million. In other words, it killed approximately 100 million people.

At the moment, Covid-19 is spreading across our planet. According to the latest scientific evidence, it infects around 60% of the population, once it becomes established in an area. Of those who are infected, 2% to 4% die. Due to the prevalence of cheap air travel, it is likely that Covid-19 will reach 90% of the world's population. Very few people nowadays, on this planet, live in isolation. If we use these figures, then we obtain the following number of dead around the world once Covid-19 has swept around the globe: 84 to 168 million people. Therefore, according to what we know, Covid-19 might kill a much smaller percentage of people than the Black Death, but Covid-19 is projected to kill as many people, in total, as the Black Death.


Historians and biologists tell us that the Black Death was able to spread across much of the planet in the 14th Century because of awful hygiene. The prevalence of open sewers and dead animals in most cities and towns created a perfect breeding ground for rats and fleas. These carriers of the disease enabled it to spread. If this is correct, then a fatal flaw in the way society functioned at that time enabled a disease to spread and flourish, and eventually kill an enormous number of people.

In our modern, twenty-first century world, we like to think that we've got everything right. A disease might spread across our planet but that's nothing do with any flaws in how we've set up our society. We have the latest technology and advanced ways to kill germs. We're doing everything right.

The only problem with this idea is that there is one aspect of our society that actively helps all coronaviruses survives and flourish. Coronaviruses are not invincible. They do not last long on wooden surfaces, due to the wood's natural antibacterial properties. Coronaviruses also do not last long in hot or humid conditions. They can also be destroyed by the ultraviolet component of sunlight, which literally smashes up their RNA component. This means that traditionally, in a natural environment, particularly in Summer, and especially in tropical or sub-tropical countries, coronaviruses can fade out rapidly. Unfortunately for our modern world, air conditioning has utterly changed the daily environment for so many people in hot countries. Instead of people moving around in a hot and/or humid environment, with sunshine and fresh air, many people move around in sealed-in, air-conditioned environments. This gives coronaviruses a huge helping hand, for a coronavirus can last for days on an inert surface in a cool, dry, shaded location. For example, the rapid spread of the virus in the Diamond Princess has been partly blamed on the ship's HVAC system, its Heating, Ventilation, and Air-Conditioning system, which may have been moving the virus's aerosol droplets around the boat.

In a previous article, I explored the effect that air-conditioning has had on the developed world, and its terrible effect on climate-change. It now has another dark trait, it has become our modern plague-vector, the aspect of our society that actively helps Covid-19 survive and spread. It is a twenty-first-century incarnation of the Black Death's open sewers and dead animals. We have progressed in much of the world, we don't have open sewers any more, but we're still making mistakes. Hopefully, we'll fix these too.