Climate Change and Pollen Allergies

• Pre-1990s: Allergy seasons and pollen levels are within historical norms.
• 1990s: Research indicates that ragweed pollen monitoring has been taking place at 11 locations in the central US and Canada since this decade as part of a national allergy monitoring network.
• 1990-2018: Research by William Anderegg finds approximately a 21% increase in overall pollen concentrations in North America.
• Since the Beginning of the 20th Century: The contiguous U.S. has experienced an increase of more than two weeks on average in the frost-free season.
• Since the 1970s: The frost-free season has expanded by an average of at least 11 days in all nine of the U.S.'s distinct climate regions.
• 1995: The US EPA begins tracking changes in ragweed pollen season length at 11 locations in the central United States and Canada.
• 1995-2015: Analysis of ragweed pollen season data shows a lengthening of the season at 10 of the 11 studied locations, with more pronounced increases at higher latitudes. Winnipeg, Manitoba, sees the largest increase at 25 days.
• 2011: A study estimates the economic impact of medically treating seasonal allergies in the United States to be $3.4 billion annually.
• 2016: A study in Sweden analyzes the economic impact of allergic rhinitis, estimating an impact of about $1.43 billion in Sweden alone due to presenteeism, absenteeism, and medical treatment.
• 2018: A study notes only 85 pollen stations operating in the U.S., highlighting a need for more comprehensive monitoring.
• 2019: The Asthma and Allergy Foundation of America reports that ragweed pollen allergy affects an estimated 15.5 percent of all Americans.
• 2019: An EPA study estimates that between 35,000 and 60,000 asthma-related emergency department visits were linked to pollen, projecting a potential 14% increase by 2090.
• Early 2020s (anecdotal): Allergists report an increase in patients seeking treatment for seasonal allergies.
• 2021: The CDC begins collecting data on the prevalence of seasonal allergies.
• April 19, 2023: Samantha Harrington publishes an article in Yale Climate Connections highlighting research by William Anderegg and Brooke Lappe on the impact of climate change on worsening pollen allergies.
• March 18, 2025: Kasha Patel publishes an article in The Washington Post detailing the "allergy capitals" of the U.S. for the previous year (2024), based on data from the Asthma and Allergy Foundation of America. Wichita, Kansas, is ranked the most challenging city.
• April 9, 2024: Bridget Balch publishes an article in AAMC News discussing how warmer temperatures and "botanical sexism" are exacerbating seasonal allergies.
• By 2050 (projected): Some computer models suggest that climate change could significantly increase airborne pollen loads, even in areas that currently have low loads.
• Ongoing: Climate change continues to cause warmer temperatures, longer frost-free seasons, increased carbon dioxide levels, and altered precipitation patterns, all contributing to longer and more severe pollen seasons and worsening allergy symptoms.