The Coronavirus-Climate-Air Conditioning Nexus
This summer, America will be hemmed in by a climate emergency on one hand and a continuing deadly pandemic on the other. Meanwhile, humming away in the background, aggravating our plight, will be that longtime summer friend: air conditioning.
Climatic models are projecting that heat waves will be more frequent and more intense than usual across the United States this summer. As pandemic-induced restrictions are relaxed, severe heat likely will drive most social gatherings and group activities into the air-conditioned indoor world. There, the risk of coronavirus spread will be much higher than it is in a park or on a porch.
These days, it’s always riskier to gather indoors than outdoors. Research says that indoor spaces can be made somewhat safer simply by opening windows for ample ventilation. That won’t work in air-conditioned buildings, which must be zipped up tight.
Air conditioning raises the risk further by lowering the indoor relative humidity. Studies show that coronaviruses in general, including those that cause the common cold, SARS and MERS, remain viable and infective longer when humidity is low, whether the viruses are in the air or on surfaces.
There’s more. When humidity is high, virus particles are carried inside bulky saliva droplets that fall to the floor or other surfaces within seconds. But with low humidity, they are in much smaller droplets called aerosols that stay airborne far longer, ready to be inhaled.
Some types of cooling systems also serve to circulate droplets very efficiently and potentially could infect large numbers of people. A widely cited case study found that in January, one customer at a restaurant in Guangzhou, China, infected nine other diners sitting at three different tables with COVID-19. The breeze from an air conditioner near one of the tables had efficiently distributed virus-laden droplets along a 20-foot-long path.