NORTHERN HEMISPHERE — AccuWeather meteorologists predict that spring 2026 pollen seasons across multiple U.S. regions will start early and be intensified by climate change. The forecast calls for high tree pollen in the Ohio River Valley and parts of the Pacific Northwest, an intense weed pollen season in the Rockies, and early spikes in grass pollen across the Northern Plains and Great Lakes in June and July, driven by high rainfall and warmer weather.

New England and parts of the Gulf South might see lower than usual tree pollen this spring due to a cooler spring and less rain, AccuWeather meteorologists said. They said the 2026 trends fit into the overall pattern of an extending allergy season due to climate change. Spring bloom arrived early across much of the United States, according to the USA National Phenology Network.

Climate change is contributing to longer and more severe pollen seasons across the Northern Hemisphere, with rising temperatures and carbon dioxide pollution worsening conditions in the United States. Global warming brings shorter winters and earlier thaws, causing trees to start flowering earlier in the spring. A 2021 study found that human-caused climate change is worsening North American pollen seasons. Climate Central found that between 1970 and 2025 the freeze-free growing season lengthened in 198 U.S. cities by an average of 21 days, with the Northwest and Southwest seeing the largest increases. A 2022 study published in Nature Communications found that high levels of carbon dioxide boost pollen production and could increase it by as much as 200 percent by the end of the century.

About a quarter of U.S. adults and one in five U.S. children have seasonal allergies, which cause itchy eyes, runny noses, and cold-like symptoms. Pollen can disrupt sleep, increase the risk of sinus infections, and cause people to miss school and work. A 2024 study based in Texas found that allergies can account for a large share of emergency department visits for asthma attacks during periods of high pollen counts.

"It's the same symptoms, just more intense," said Moshe Ben-Shoshan, a pediatric allergist. Some of his patients are experiencing stronger allergy symptoms than in the past and cannot control them with antihistamines or nasal sprays that used to work.

David Wees, a faculty lecturer in horticulture at McGill University in Montreal, said summer ragweed flowers longer and extends pollen season into the fall as climate change delays the first winter frosts across much of North America. Wees, who suffers from seasonal allergies, has noticed his symptoms starting earlier and lasting longer. "There's a couple birch trees outside my office," he said. "I know it because my nose feels stuffy and my eyes feel itchy." He also said drought can prolong pollen presence in the air because without rain to wash pollen out, it can remain airborne for weeks.

Dr. Neelima Tummala, an ear, nose, and throat doctor at NYU Langone Health, said people with allergies are sensitive to other respiratory triggers such as heat waves and increased air pollution, and that mold allergies can flare up after climate-driven disasters like hurricanes or in homes without proper ventilation. On days with heavy wildfire smoke from Canada, her patients experience the effects of multiple respiratory stressors. During one period of heavy smoke last summer, a patient told her they were afraid to go outside. "That's just really sad. That's not how you should live your life," Tummala said. "It's a modifiable risk factor. Climate change is something we can do something about."