Warmer Growing Season, Longer Allergy Season

Analysis of USA National Phenology Network data shows that first spring leaves now emerge earlier in 88% of 242 major U.S. cities, shifting by an average of six days since 1981. This trend, combined with a freeze-free growing season that has stretched 21 days longer on average across 173 cities between 1970 and 2025, extends allergy seasons and increases the risk of 'false spring' crop losses. Ecological disruptions include potential mismatches between bird migration and the peak abundance of food sources.

• Between 1981 and 2025, the first leaves of spring emerged earlier in 88% (212) of 242 major U.S. cities, with an average shift of six days earlier. The most significant shifts occurred in the Northeast, Ohio Valley, and Southeast, with New York City and Newark, NJ seeing the earliest emergence, 16 days earlier than in the early 1980s.
• The freeze-free growing season across 173 major U.S. cities increased by an average of 21 days from 1970 to 2025, which extends the period plants release pollen and worsens seasonal allergies for approximately one-quarter of U.S. adults and one-fifth of children.
• Earlier spring leaf-out increases the risk of 'false springs,' where a hard freeze follows early growth. A 2017 false spring in the southeastern U.S. resulted in approximately $1 billion in fruit crop losses. Future risks may increase in the Midwest and Great Plains if heat-trapping pollution rises.
• Warming trends disrupt ecological timing, such as causing birds in the contiguous U.S. to migrate earlier, which may lead to a mismatch between the birds and the peak abundance of the insects they eat or the flowers they pollinate.

APA

Crimmins, T. M. (2026). Warmer Growing Season, Longer Allergy Season. Climate Central. https://www.climatecentral.org/climate-matters/earlier-spring-2026

Chicago

Crimmins, Theresa M. Warmer Growing Season, Longer Allergy Season. Climate Central, 2026. https://www.climatecentral.org/climate-matters/earlier-spring-2026.

Wikipedia

{{cite report |last1=Crimmins |first1=Theresa M. |title=Warmer Growing Season, Longer Allergy Season |publisher=Climate Central |date=11 March 2026 |url=https://www.climatecentral.org/climate-matters/earlier-spring-2026 |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{crimmins2026warmer, author = {Crimmins, Theresa M.}, title = {{Warmer Growing Season, Longer Allergy Season}}, institution = {Climate Central}, year = {2026}, month = mar, url = {https://www.climatecentral.org/climate-matters/earlier-spring-2026}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }