By Jia You

As Chicagoans brace themselves for another peak asthma and allergy season, a national report ranks the Windy City among America’s top 10 “sneeziest and wheeziest” cities. And the report, released Wednesday, blames climate change for making things worse.

The Natural Resources Defense Council (NRDC) identified 35 American cities suffering most from ragweed pollen and ozone pollution, triggers for respiratory diseases such as asthma and hay fever. Chicago ranked sixth on the list, just behind warmer southern cities such as Richmond, Virginia, and Memphis, Tennessee. Oklahoma City, Philadelphia and Chattanooga, Tennessee round out the top six.

The American Lung Association’s State of the Air 2015 report, released in April, gave Cook County an “F” grade for ozone pollution.

“It’s the overlap of the ozone problem and the pollen problem,” said Henry Henderson, the NRDC’s Midwest director and Chicago’s former environment commissioner. “As we are looking forward to what will happen with climate change, which is exacerbating these problems, that’s the double-whammy that puts us at Number Six.”

Asthma and allergies affect one in five Americans, according to estimates from the Asthma and Allergy Foundation in America. And climate change is making things worse for these patients, according to the NRDC report. As global temperature increases, springs thaws occur earlier and plants such as ragweed pollinate more, said Samantha Ahdoot, a pediatrician in Alexandria, Virginia. The change particularly affects northern cities and regions, where the allergy season has grown by 20 days over the past two decades, she said.

Ragweed pollens cause both hay fever — inflammation of the nasal airways — and asthma symptoms, said Anne Ditto, an associate professor in medicine, allergy and immunology at Northwestern University’s Feinberg School of Medicine.

“Ragweed is a major allergen that we have in the Midwest,” she said. “With the warmer weather you have longer seasons of pollination, and the plants pollinate more, so people who are allergic are being exposed to higher levels for a longer time.”

Warmer summers also create ozone smog in cities, which can trigger lethal asthma attacks, said Brian Urbaszewski, environmental health programs director at the nonprofit Respiratory Health Association of Metropolitan Chicago. A pungent gas, naturally occurring ozone forms a belt above Earth, known as the ozone layer, and shields people from harmful ultraviolet radiation. But ozone smog at the ground level — created when exhaust from cars, factories and fossil fuel power plants cook in the sun — irritate the airways and trigger respiratory diseases.

“It burns the insides of your lungs,” Urbaszewski said. “For someone with asthma this can be a terrifying experience, as lung muscles spasm and close up, preventing breathing.”

Addressing these problems requires national initiatives, Henderson said.

“This isn’t just a City of Chicago problem. A lot of the stuff from Central Illinois coal plants is blowing over to Chicago and contributing to our ozone levels here,” he said. That’s why it’s really important that we look at this from a national perspective.”

He urged Chicagoans to support the Environmental Protection Agency’s Clean Power Plan, a set of standards addressing carbon emissions from power plants that will be released this summer, as well as a Clean Jobs Act introduced by Illinois legislators in February that would ramp up the state’s renewable energy standard.

“It’s really critically important that we take the measures that we need to take now to protect the planet for our children in the future”, said Kelly Nichols, a mother of two whose son suffers seasonal allergies, and an Illinois field organizer for Moms Clean Air Force.