The coronavirus crisis was already bad. Extreme heat waves are making it worse.

Climate pollution is making heat waves longer, hotter and more frequent. As communities throughout the United States face surges in COVID-19 infections, the extreme heat is creating additional public health challenges, with sweltering conditions complicating efforts to contain the virus and leading to a cascade of difficult choices.

The current heat wave across the South and Southwest has seen heat warnings and advisories for at least 11 states, stretching from Southern California to the Florida Panhandle. Last weekend in Phoenix, temperatures hit a record high of 116 degrees Fahrenheit on Sunday, July 12—and were measured at or above 110 degrees for at least ten consecutive days.

This is part of a long-term upward trend in global temperatures caused by climate pollution. Over the last 60 years, each decade has been decisively warmer than the previous one. The number of deadly heat waves in 50 major cities across the U.S. has increased dramatically from an average of two heat waves per year during the 1960s, to more than six per year during the 2010s.

Now layer in a deadly pandemic. What happens when searing heat descends on a city where residents are asked to stay in their homes to avoid spreading a deadly disease?

The most vulnerable people will bear the brunt

Up to a quarter of all American households don’t have access to air conditioning, and they are often the poor and the elderly, for whom coronavirus poses the greatest risk. Moving them to crowded cooling centers — like public libraries, community centers and senior centers — increases the likelihood of exposing and possibly killing those most vulnerable to the disease.

Consider, too, the millions of Americans who work outdoors — who, for example, deliver mail or labor on highway construction crews as temperatures soar and heat waves worsen. These conditions set up an impossible choice between a person’s health and the job that feeds their family.

Then there are the 25 million Americans with asthma: As temperatures climb and heat waves become more frequent, the metaphorical rope around their chests will tighten. Heat and humidity encourages mold growth and seasonal pollen, which are asthma triggers. On very hot days, the problem of ozone pollution – which happens when heat and sunlight combine with pollutants to create ozone – also increases. Ozone causes damage to everything from human lungs to crop yields. While this is especially worrisome for people with asthma and related illnesses, ozone is bad for all people’s health, triggering problems including chest pain and coughing. It can also harm lung tissue and reduce lung function, which is especially worrisome amid the threat of COVID-19, which itself can cause serious lung damage.

Because the burden of asthma is strongly related to social and economic status, access to health care and exposure to environmental triggers, the most vulnerable are most at risk here, too. African Americans, Latinos, and the poor—particularly poor children—have a higher incidence of the illness.

Heat waves can be lethal

If you think putting up with a spell of hot weather is not a big deal, look at recent history. In France, record heat waves in June and July 2019 killed more than 1,400 people. In India, an intense heat wave in 2015 killed more than 2,300 people and had temperatures hot enough to melt pavement in New Delhi.

All across the United States, temperatures are climbing. According to a study by the Union of Concerned Scientists, the number of days in Minnesota with a heat index above 90 degrees could quadruple by around mid-century if no action is taken to climate pollution. And in Florida, the average number of days when the heat index is 105 degrees or higher is projected to increase more than five times by then — from 25 dangerous heat days a year to 130 — more than any other state.

There are also agricultural and economic impacts. Rising temperatures increase the likelihood of droughts and spread insect borne diseases. They will also have a profound impact on outdoor recreation and sports — heat is already a leading cause of death and disability among high school athletes.

The challenges of COVID-19 and climate pollution are connected

Families should not have to decide between keeping their elderly relatives at homes, without air conditioning, and the risking their exposure to the virus. We have to tackle both health threats — defeating the immediate threat of COVID-19, while also dramatically reducing the pollution that’s heating up the planet. That means transitioning to clean energy, electrifying transportation, putting limits on pollution and prioritizing communities that carry the highest burden and health disparities.

As we move to repair the COVID-battered economy, we have a chance to make it better than it was before. In the U.S., we can rebuild better by investing in clean energy to create more jobs and less pollution. In doing so, we’ll reduce shocks to the system from the global pandemic to devastating heat waves made worse by climate change.

It’s time to act.