While there is some preliminary evidence that sunlight, heat and humidity could slow the spread of the coronavirus, the summer months also promise a host of new risks, The Washington Post reports. Soaring temperatures will either compel people wanting relief to go outside, where they could catch the coronavirus, or the coronavirus will force people to stay indoors, where they could swelter. Both the pandemic and extreme heat pose a mortal risk to the elderly and the infirm.

Experts say that climate change will likely compound the problem. Much of the country can expect unusually high temperatures this summer, relative to average temperatures between 1981 and 2010. The projections, from the National Weather Service, are consistent with the long-term warming trend. The northeast, which has been hit hard by the coronavirus, faces an especially high risk of warmer weather. No part of the country is looking forward to an unusually cool summer.

This map shows the likelihood that different parts of the country will see above-average temperatures from May through July, compared to the average from 1981 to 2010. Source: National Weather Service

It won’t be possible to determine the role of climate change until after the season has passed, experts say. The forecast of an exceptionally balmy summer comes as no surprise, given that since 1980, the contiguous United States has warmed close to 1 degree C, according to data from NOAA.

“Every summer that we have is taking place in a world in which global warming is already occurring,” said Justin Mankin, a climate scientist at Dartmouth University, adding that climate change is upping the odds of severe summer heat. “We have pretty good evidence that extreme temperatures are increasing faster than average temperatures due to global warming,” he said.

One reason is that warmer weather is drying out soil early in the season, making it hotter later on. When the soil is moist, some of that moisture evaporates, cooling off the ground, but when the soil is dry, the ground stays warm.

Climate change is also producing more days that are both hot and humid, said Radley Horton, a climate scientist at Columbia University. As oceans warm, more seawater is evaporating, turning the air more humid, which is making hot days more miserable.

“One thing that worries us about really extreme heat and humidity is that if the air becomes humid enough, it’s basically impossible for somebody to stay cool,” Horton said. When you sweat, the water on your skin evaporates, cooling you off. But when it’s muggy out, the air is already saturated, so the sweat just clings to your skin. If it’s humid enough, healthy people can die in heat waves because they cannot cool off.

“From a summer standpoint, the things that I think are going to be really damaging are the combined heat and humidity events,” Mankin said. “For the same temperature, New York has a higher incidence of heat-related mortality than Arizona does. And the reason is because when heat hits New York City, it comes with humidity.”

New York’s Central Park draws crowds in the summer. Source: sightalks via Wikipedia

Crucially, heat waves don’t pose the same risk to all people. “They affect the most vulnerable among us, just like COVID-19,” Mankin said. “The ability to cool yourself is increasingly a sign of wealth.”

Heat waves are often more severe in low-income communities and communities of color because these neighborhoods tend to lack trees or parks that would help keep the temperature low. People in these communities are also less likely to own air conditioners, and those that do may leave their air conditioners off to avoid high power bills, Horton said.

“There are a lot of people who don’t have their own air conditioners. Are they going to be able to get to cooling centers? Are the cooling centers going to be open?” he said, pointing to lockdown measures that have kept people indoors. “Some people rely on going to the beach or going to public pools to cool off as well. Is that option going to be there?”

Communities of color are facing both more cases of the coronavirus and higher levels of pollution, which is significant, given that coronavirus sufferers living in polluted areas are more likely to die of the disease. Severe heat will compound these risks both by worsening pollution and by weakening the body’s defenses.

“It puts a large strain on people’s bodies and can make it so that, if you’re also harboring a viral infection, you’re going to do a lot worse against that viral infection,” said Jeffrey Shaman, professor of environmental health sciences at Columbia University.

Shaman said the relationship between weather and the coronavirus is poorly understood, making it difficult to know where to seek relief during a heat wave. If the virus fares worse in heat and sunlight, as some research indicates, then people may be better off crowding together in the park than they would retreating to an air conditioned restaurant or movie theater, however sparsely crowded. But if the virus tolerates heat and humidity better than early findings suggest, then the park could become a petri dish.

“Unfortunately, there are so many little unknowns about this, many of which stem from the fact that we just don’t understand a lot about respiratory viruses in general, let alone COVID-19,” Shaman said. Either way, severe heat complicates the problem by forcing people to choose between suffering indoors or risking infection outdoors.

“Heat waves are only going to make it more difficult,” Shaman said. “Then you’re contending with more than one problem at the same time.”

Jeremy Deaton writes for Nexus Media, a nonprofit climate change news service. You can follow him @deaton_jeremy.