NATION – For the millions of Americans who suffer from seasonal allergies, a new study offers little to celebrate. The findings, published in the Proceedings of the National Academy of Sciences, provide compelling evidence that climate change is driving significant increases in the length and severity of pollen seasons across North America.
The research, conducted by a team led by William Anderegg of the University of Utah, represents the most comprehensive analysis to date of long-term pollen trends across the continent. By examining data from 60 monitoring stations in the United States and Canada over a 28-year period (1990-2018), the study paints a clear and concerning picture.
Three key findings emerge from the data: first, pollen seasons are starting an average of 20 days earlier than they did in 1990. Second, they are lasting an average of 10 days longer. Finally, the amount of pollen in the air has increased by an average of 21% over the study period.
These changes were consistent across all pollen types monitored, including tree species like oak and birch, as well as ragweed, a particularly potent allergen. The implications for public health are significant, as earlier, longer, and more intense pollen seasons mean increased exposure and sensitization risk for allergy sufferers.
To understand the role of climate change in driving these trends, the researchers employed statistical modeling to compare observed changes with those predicted under different climate scenarios. The results suggest that human-driven climate change was responsible for approximately half of the observed lengthening of pollen seasons and around 8% of the increase in pollen concentrations.
“These findings show that climate change isn’t just a future threat to our health – it’s already affecting millions of Americans today,” said Anderegg. “As temperatures continue to rise, we can expect these pollen trends to worsen, leading to more intense allergy seasons and increased public health impacts.”
The study adds to a mounting body of evidence linking climate change to worsening pollen seasons worldwide. A 2019 global analysis led by Lewis Ziska of the US Department of Agriculture found significant increases in both pollen loads and season duration across multiple continents, with temperature increases strongly correlated with longer pollen seasons.
More recently, a 2022 review published in Nature Reviews Allergy synthesized findings from over 150 scientific studies, concluding that climate change is unequivocally exacerbating pollen seasons and allergic respiratory diseases on a global scale. The review highlighted multiple climate-driven changes, including earlier pollen season onsets, increased pollen production and allergenicity, and shifts in the geographic distribution of allergenic species.
For the more than 24 million Americans who suffer from seasonal allergic rhinitis (hay fever), these changes have serious consequences. Allergies can significantly impact quality of life, leading to missed work and school days, reduced productivity, and increased healthcare costs. A 2021 analysis estimated that emergency room visits and hospitalizations for pollen-induced asthma alone cost the US nearly $500 million per year.
Children bear a particularly heavy burden, as allergies can impair learning, worsen asthma risk, and lead to more frequent school absences. On a global scale, allergic diseases already affect up to 30% of the population, with prevalence expected to reach 50% in some European countries in the coming decades.
Despite the growing body of evidence and the high societal costs, experts say that public awareness of the climate-allergy link remains low, and policy responses have been insufficient. Pollen monitoring infrastructure is sparse in many regions, and few jurisdictions have integrated pollen data into their climate adaptation or public health planning.
“This study should serve as a wake-up call,” said Jeffrey Demain, director of the Allergy, Asthma, and Immunology Center of Alaska and a co-author on the paper. “We need to do more to educate the public about the health risks of climate change and to prepare our healthcare systems for longer, more severe allergy seasons.”
The authors say their findings underscore the need for expanded pollen monitoring, standardized data collection and reporting, and better integration of pollen data with local climate and health monitoring systems. Such efforts could help individuals and healthcare providers better anticipate and manage the impacts of changing pollen seasons.
On a personal level, experts advise allergy sufferers to take proactive steps such as limiting outdoor activities during high pollen days, using HEPA filters to improve indoor air quality, and working with their healthcare providers to optimize medication and immunotherapy regimens.
However, they stress that individual adaptation measures can only go so far and must be coupled with concerted efforts to address the root cause of the problem: climate change.
“Pollen is just one of many health hazards that will worsen as the world continues to warm,” said Amir Sapkota, a professor at the University of Maryland School of Public Health who studies the health impacts of climate change. “Tackling climate change isn’t just about protecting our environment – it’s about safeguarding our health and our future.”
-Stephan Lightman
