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.
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