The heat dome that is scorching more than 90 million people across the United States this week also threatens to deliver polluted air, something that scientists say is a growing problem on a warming planet.
Researchers are increasingly worried about the twin health hazards of extreme heat and pollution, which can amplify each other. As climate change drives up global temperatures past record levels, the frequency of days when it is both hot and polluted has also been increasing.
“We’re in the middle of a bad air quality summer in a lot of the country,” said Joseph Goffman, who led the Office of Air and Radiation at the Environmental Protection Agency during the Biden administration. “And now it’s more likely than not that we’ll see summers like this in the coming years.”
Several factors are converging to amplify health risks during sweltering days. Extreme heat can trap polluted air in place, so it does not dissipate. Climate change is making wildfires more frequent and intense, pumping smoke into the atmosphere and contributing to the reversal of a decades-long trend of air quality improvement in some parts of the United States.
And the Trump administration is moving to weaken limits on emissions from power plants and cars, which could increase carbon dioxide, sulfur dioxide, particulate matter and other pollutants. It is also encouraging more mining and burning of coal, the dirtiest of the fossil fuels.
Even as heat can make air pollution worse, the combination of the two environmental hazards can have outsize effects on public health, experts say. Multiple cities warned of air quality this week that is unhealthy for sensitive groups, including New York City, Philadelphia, Cincinnati and Grand Rapids, Mich.
A 2023 analysis of more than 20 million deaths across the world found that hot days and days with bad air quality both resulted in higher-than-normal mortality rates. But periods in which heat and pollution are combined were even more deadly.
The combination can be particularly stressful for children, older people or anyone with respiratory diseases like asthma. Dr. Mary Rice, director of the Center for Climate, Health and the Global Environment at the Harvard T.H. Chan School of Public Health, called the phenomenon a “double whammy” that can result in increased hospital admissions.
“I think of heat as especially bad for the brain, for cardiovascular and mental health admissions,” she said. “Air pollution is very harmful for respiratory and cardiovascular admissions and also stroke. Those together can further enhance cardiovascular and respiratory risk.”
How heat worsens air quality
Heat waves are primarily caused by high-pressure systems that trap warm, stagnant air.
“Basically, you’ve got this big cooking pot,” said Jim McQuaid, an atmospheric chemist at the University of Leeds. Without wind to blow pollutants away, they stay in one area and intermingle in a process that Dr. McQuaid compared to stirring a sauce.
“You’ve got all of the ingredients going in, then you’ve got heat going in, and it just all cooks,” Dr. McQuaid said. Like a sauce reducing in a pot, he added, the mixture slowly grows stronger and more potent. In urban areas, the heat island effect can add to this buildup.
There are two main types of air pollution that experts track for their effects on human health: ground-level ozone and particulate matter.
Summer days tend to see higher concentrations of ground-level ozone, a powerful pollutant that forms through chemical reactions near the ground. Ozone irritates the lungs and can cause coughing and shortness of breath. Its formation is accelerated under hot and sunny conditions, and a buildup of emissions from the burning of fossil fuels can also contribute.
Particulate matter refers to tiny pieces of solids and liquids in the air, all smaller than a grain of sand or a strand of human hair. When inhaled, the fine particles, known as PM 2.5, can reach the deepest part of the lungs and pass into the bloodstream, causing harm throughout the body, including the heart, lungs and brain.
The World Health Organization estimates that outdoor and indoor air pollution combined cause 6.7 million premature deaths a year, with most of those deaths occurring in low- and middle-income countries.
Extreme heat can also contribute to the conditions that make wildfires more severe. Wildfire smoke contains particulate matter, and can travel for thousands of miles. A 2024 study found that wildfire smoke may have killed as many as 12,000 Californians prematurely in 2018.
“The intensity of that exposure tends to be quite high,” said Dr. Meredith McCormack, director of pulmonary and critical care at Johns Hopkins University and a representative of the American Lung Association. She added that metals and chemicals blend into that smoke when buildings burn. “You have a mixture of natural and man-made sources often during wildfire events at levels that are really extraordinary.”
Regulatory rollbacks
President Trump and Republicans in Congress are working to roll back various restrictions on air pollution, and the administration has canceled grants that support research on the health effects of heat and air pollution.
The Environmental Protection Agency is reconsidering limits on tailpipe emissions from cars and light trucks, and Senate Republicans are eyeing ways to revoke them as well.
The Senate also blocked California’s plans to implement clean air standards that would have phased out the sale of new gas-powered cars by 2035.
This month, the E.P.A. moved to weaken limits on emissions from power plants, including greenhouse gases and air pollutants like mercury, arsenic and gas. The rules were expected to force coal plants to effectively eliminate greenhouse gas emissions or shut down.
Taylor Rogers, a White House spokeswoman, said the Biden-era regulations were “harmful and stifling our energy industry.”
“Recent events are further proof that restoring America’s energy independence is critical to our economic and national security,” Ms. Rogers said in a statement.
In a statement, the E.P.A. said the regulatory moves were part of the agency’s “core mission of protecting human health and the environment.”
The Trump administration has been promoting the production and use of oil, gas and coal, the burning of which is the main driver of climate change. Mr. Trump has been especially focused on trying to revive the flagging coal industry, ordering one coal-fired power plant in Michigan to stay open just days before it was scheduled to permanently close. The order came as a surprise to the plant operators.
“The continued operation of coal-fired power plants is harmful to the health of those communities,” Dr. Rice said. She added that there was “very clear evidence” that pollutants from coal emissions increased the risk of asthma and could be deadly.
The Trump administration’s cuts to government spending have also hit studies examining how to protect Americans from the health effects of air pollution and extreme heat.
Two of Rice’s studies have been affected. For one, researchers planned to install air-conditioners for older adults with chronic diseases as part of an effort to determine whether the units would help relieve heat-related stress.
Another study looked at whether installing air purifiers would improve health outcomes for former smokers with chronic obstructive pulmonary disease. The trial is in its final stretch, but Rice lost $500,000 for the last year of work.
Claire Brown covers climate change for The Times and writes for the Climate Forward newsletter.
The post Extreme Heat Is Exacerbating Air Pollution, a ‘Double Whammy’ for Health appeared first on New York Times.
