POLLEN PROBLEMS: Climate Change, the Growing Season, and Americas Allergies

Climate change is extending the freeze-free growing season in the United States, leading to longer periods of pollen exposure for nearly 20 million allergy sufferers. Analysis of 201 cities shows that 83% experienced longer growing seasons since 1970, with the most significant increases in the western U.S. Additionally, rising atmospheric CO2 levels are shown to increase the quantity and allergenicity of pollen from plants like ragweed.

• Climate change is extending the freeze-free season, which allows plants more time to grow and produce pollen. Analysis of 201 U.S. cities reveals that 83% have seen their freeze-free seasons lengthen since 1970, with the average city experiencing an increase of just over two weeks.
• The lengthening of the growing season is most pronounced in the western United States, increasing by approximately 19 days in the Southwest and 16 days in the Northwest relative to early twentieth-century averages. Some cities, such as Bend and Medford in Oregon and Las Cruces in New Mexico, saw increases of at least two months.
• Rising atmospheric carbon dioxide (CO2) levels directly increase the volume and potency of allergenic pollen. For ragweed, pollen production more than doubled as CO2 concentrations rose from 280 to 370 parts per million between 1900 and 2000. If CO2 reaches 600 parts per million, ragweed pollen could become approximately 1.7 times more allergenic than it was in 2000.
• The prevalence of allergies and asthma in the U.S. has increased significantly. Hay fever affected about one in ten Americans in 1970, rising to three in ten by 2000. Asthma rates rose from 3.1 percent to 8.4 percent of the population between 1980 and 2010, with higher rates among children, low-income households, and African-Americans.
• Allergies impose a significant economic and health burden on the United States, costing more than $18 billion annually. In 2015, asthma resulted in 1.7 million emergency room visits, and in 2016, it caused approximately 3,500 deaths.

APA

Climate Central (2019). POLLEN PROBLEMS: Climate Change, the Growing Season, and Americas Allergies. https://www.climatecentral.org/report/report-pollen-allergies-climate-change

Chicago

Climate Central. POLLEN PROBLEMS: Climate Change, the Growing Season, and Americas Allergies. 2019. https://www.climatecentral.org/report/report-pollen-allergies-climate-change.

Wikipedia

{{cite report |author=Climate Central |title=POLLEN PROBLEMS: Climate Change, the Growing Season, and Americas Allergies |date=27 March 2019 |url=https://www.climatecentral.org/report/report-pollen-allergies-climate-change |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{climatecentral2019pollen, author = {{Climate Central}}, title = {{POLLEN PROBLEMS: Climate Change, the Growing Season, and Americas Allergies}}, institution = {Climate Central}, year = {2019}, month = mar, url = {https://www.climatecentral.org/report/report-pollen-allergies-climate-change}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }