At a Glance
- Cases of COVID-19 are surging in places where the weather is hot.
- So far, it's unclear how seasonal temperatures affect the virus.
- Two recent studies show air conditioning systems could spread infected droplets.
COVID-19 cases are spreading fastest in places where the weather is hot, including Florida, and Arizona and Texas.
The surge in infections comes as summer heat kicks off and more people are spending time outside, but also closing their windows and turning on air conditioners.
That's led some scientists to wonder if the heat, or the air conditioning, have any effect on the transmission of coronavirus. It's also dashed any hopes that the infections would wane in the summertime, like cases of the flu and the common cold do.
"As I reflect on the early months of the pandemic, places like Florida and Arizona were already experiencing record-breaking heat, and NOAA’s Climate Prediction Center predicted a warmer than normal summer for most of us," Dr. Marshall Shepherd, director of the University of Georgia’s atmospheric sciences program and a leading international expert in weather and climate, said in a column he wrote for Forbes this week. "As an atmospheric scientist and professor, those early indications were not encouraging to me."
So far, there's no solid research to show whether or not seasonal changes affect the virus.
"It is not yet known whether weather and temperature affect the spread of COVID-19," the U.S. Centers for Disease Control and Prevention said on its website. "There is much more to learn about the transmissibility, severity and other features associated with COVID-19 and investigations are ongoing."
The World Health Organization said extremely cold weather doesn't seem to impact the virus, either.
But two recent studies indicate that air conditioning could help spread the disease.
One examined a coronavirus outbreak in 10 people from three unrelated groups who all ate at a restaurant in Guangzhou, China, at the same time. The incident happened in January, and one of the families had just traveled from the central Chinese city of Wuhan, where the pandemic began late last year.
Researchers looked at how long the three groups were in the restaurant and where they sat in relation to each other, as well as airflow and other considerations. The results were posted this month on the CDC website.
"We conclude that in this outbreak, droplet transmission was prompted by air-conditioned ventilation," wrote Jianyun Lu, lead author of the study and deputy chief of the Department of Control and Prevention for Infectious Disease at the Guangzhou Center for Disease Control and Prevention. "The key factor for infection was the direction of the airflow."
Another study, published earlier this year in the journal M Systems, recommended paying particular attention to maintenance and proper installation of filters in heating, ventilation and air conditioning systems in order to help reduce the transmission of droplets in the air.
Health experts also agree it's clear that the virus is spread more easily in confined, indoor spaces with windows and doors closed.
"While studies continue to emerge, it probably is not a bad idea for public facilities to evaluate HVAC systems ... Nothing is conclusive at this point, but it sure couldn’t hurt as states continue to 'open up,'" Shepherd said.
The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.