This summer, daytime temperatures topped 100 degrees for a full month in Phoenix. In northwest China, temperatures soared above 125 degrees. Southern Europe withstood waves of 100-plus degree days. Wrapped together, heat waves illustrate a sobering reality: human-driven climate change is making extreme heat worse worldwide. But health-threatening heat isn't the only outcome of record-breaking weather: air pollution spikes when the temperatures rise according to a new report from the World Meteorological Organization.

"Climate change and air quality cannot be treated separately. They go hand in hand and must be tackled together to break this vicious cycle," WMO Secretary General Petteri Taalas said in a press release.

The new report, which focuses on 2022, highlights the growing risk of air pollution connected to wildfires. Hotter temperatures increase the risk of large, hot-burning fires, which can pump enormous plumes of smoke into the air. That smoke causes health problems near the fire but also for people thousands of miles downwind.

Emergency room visits for asthma spike during and after smoke exposure. Heart attacks, strokes, and cognitive function problems also increase after smoke exposure. In 2022, people living in the Amazon basin, Alaska, and the western part of North America all breathed in more wildfire smoke than they have on average over the past 20 years.

Extreme heat also drives up the likelihood of drought, which in turn makes big dust storms more likely. Enormous clouds of fine dust wafted off major deserts last year, particularly affecting the Arabian Peninsula region. Southern Europe also got hit by a major dust storm after a heat wave baked the deserts of northern Africa in the summer.

Hot air temperatures also encourage the development of ozone — a clear, odorless gas that irritates people's lungs. It's the main component of smog. Ozone forms when pollutants, often from the burning of fossil fuels, react with heat and sunlight. It forms both high in the atmosphere, where it helps protect the planet from ultraviolet radiation from the sun, and near the ground, where humans live and breathe.

When people breathe ozone in it can worsen health problems like bronchitis or even heart conditions. Hot, stagnant air–exactly the conditions common during heat waves–makes ozone pollution worse. A massive, deadly heat wave in July of 2022 sent ozone concentrations across southern Europe well into unhealthy levels for weeks, the report says.

"That's a very bad combination of conditions," says Julie Nicely, an atmospheric chemist at the University of Maryland, College Park, who worked on the report. That mix is particularly dangerous for elderly people, or people with breathing sensitivities. "That is very bad for the lungs and the cardiovascular system. It's just very unhealthy," she says.

Air pollution levels have dropped across the Northern Hemisphere in the past few decades in response to environmental regulations like the Clean Air Act in the United States. Ozone pollution, however, remains a problem. The report authors point out that the extra heat in the atmosphere driven by climate change overpowers even the gains made by stringent environmental protections. The authors said that underscores the importance of slowing or reversing human-caused climate change as quickly as possible.