The Growing Allergy Burden
Climate change is contributing to longer and more severe pollen seasons across the Northern Hemisphere, with rising temperatures and carbon dioxide pollution driving the trend [1][3]. About a quarter of U.S. adults and 1 in 5 children have seasonal allergies, and the changing climate is making their symptoms worse [2].
Earlier Springs, Longer Seasons
Spring bloom arrived early across much of the United States in 2026, according to the USA National Phenology Network [5]. Climate Central found that between 1970 and 2025, the freeze-free growing season lengthened in 198 U.S. cities analyzed, with an average increase of 21 days [11]. A 2021 study confirmed that human-caused climate change is worsening North American pollen seasons [10].
Regional Predictions for 2026
AccuWeather predicts high tree pollen levels in the Ohio River Valley and parts of the Pacific Northwest in spring 2026 [6]. Early spikes in grass pollen are expected in the Northern Plains and the Great Lakes in June and July due to high rainfall and warmer weather [7]. An intense weed pollen season is forecast for the Rockies [8]. In contrast, lower than usual tree pollen levels are expected in New England and parts of the Gulf South due to a cooler spring and less rain [9].
How CO2 Boosts Pollen
High levels of carbon dioxide boost pollen production directly, potentially increasing it by up to 200% by the end of the century, according to a 2022 study [12]. Pollen counts are rising globally, particularly well studied across North America and northern Europe, said Moshe Ben-Shoshan [13]. Some of his patients are experiencing stronger symptoms than in the past and cannot control them with treatments that used to work [14].
Extended Allergy Seasons
As climate change delays first winter frosts across much of North America, summer ragweed keeps flowering longer, extending pollen season into fall, said David Wees [15]. Increased humidity, heat and flooding create ideal conditions for mold to flourish in places where it was previously rare [16]. A 2024 study based in Texas found that high pollen counts account for a significant portion of emergency department visits for asthma attacks [17].
Compound Effects
Climate-change-driven heat waves, air pollution and natural disasters can exacerbate allergy symptoms [4]. People with allergies are also sensitive to other respiratory triggers such as heat waves and increased air pollution, said Dr. Neelima Tummala [18]. Drought is another climate-intensified problem; rain typically washes pollen out of the air, without it pollen can blow around for weeks, said David Wees [19].
What to Watch Next
As global temperatures continue to rise, pollen seasons are expected to start earlier, last longer, and become more intense, with regional variations depending on local weather patterns. Monitoring early spring bloom and seasonal forecasts will be key for allergy sufferers to prepare.