Seasonal allergies: pollen and mold

Climate change is extending the U.S. allergy season through warming temperatures and increased CO2, which stimulate allergen production and lengthen the freeze-free growing season. These trends increase health risks, particularly for asthma sufferers, and contribute to significant economic costs. The document highlights regional variations, the role of 'thunderstorm asthma,' and the disproportionate impact on low-income and minority communities.

• Climate change is extending the duration and intensity of allergy seasons in North America. A study noted that from 1990 to 2018, pollen seasons lengthened by an average of 20 days and concentrations increased by 21%, with human-caused warming responsible for approximately half of the shift toward earlier seasons.
• Analysis of 203 U.S. cities since 1970 shows the freeze-free season is lengthening on average by 15 days. This trend is most pronounced in the West, where the season lengthened by 27 days, followed by the Southeast (16 days), Northeast (15 days), South (14 days), and Central region (13 days). Reno, Nevada, saw an increase of 99 days.
• Increased atmospheric carbon dioxide (CO2) stimulates plant growth, which can intensify allergen production. Modeling suggests that under high greenhouse gas emission scenarios, CO2 could double pollen production by the end of the century and cause the season to start up to 40 days earlier and last up to 19 days longer.
• Warming winters may increase exposure to mold allergens. Analysis of 232 U.S. locations since 1970 indicates that winter is the fastest-warming season, with 80% of those locations experiencing at least seven more days above the 19912020 winter normal temperature than in 1970.
• Thunderstorms can trigger 'thunderstorm asthma' by breaking pollen and mold spores into smaller, more easily inhaled particles. This phenomenon has led to overwhelmed emergency rooms, such as in Melbourne in 2016.
• Seasonal allergies and asthma impose a significant economic burden in the U.S., with total allergy costs exceeding $18 billion annually. Between 2008 and 2013, the annual medical cost of asthma was over $3,200 per person. These costs disproportionately affect low-income families and minority communities (Black, Hispanic, and American Native/Alaskan Native).
• In the San Francisco Bay Area, pollen and mold seasons lengthened by approximately eight and nine weeks, respectively, between 2002 and 2019, though overall annual counts decreased, possibly due to land use changes and urbanization.

APA

Climate Central (2023). Seasonal allergies: pollen and mold. https://assets.ctfassets.net/cxgxgstp8r5d/6HEq6ZLb0QpvXxScvaM7sc/4c67f48bec857b55f3c02a072cc606e9/FINALSeasonal_allergies_pollen_and_mold_2023__EN_.pdf

Chicago

Climate Central. Seasonal allergies: pollen and mold. 2023. https://assets.ctfassets.net/cxgxgstp8r5d/6HEq6ZLb0QpvXxScvaM7sc/4c67f48bec857b55f3c02a072cc606e9/FINALSeasonal_allergies_pollen_and_mold_2023__EN_.pdf.

Wikipedia

{{cite report |author=Climate Central |title=Seasonal allergies: pollen and mold |date=March 2023 |url=https://assets.ctfassets.net/cxgxgstp8r5d/6HEq6ZLb0QpvXxScvaM7sc/4c67f48bec857b55f3c02a072cc606e9/FINALSeasonal_allergies_pollen_and_mold_2023__EN_.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{climatecentral2023seasonal, author = {{Climate Central}}, title = {{Seasonal allergies: pollen and mold}}, institution = {Climate Central}, year = {2023}, month = mar, url = {https://assets.ctfassets.net/cxgxgstp8r5d/6HEq6ZLb0QpvXxScvaM7sc/4c67f48bec857b55f3c02a072cc606e9/FINALSeasonal_allergies_pollen_and_mold_2023__EN_.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }