Longer Allergy Seasons Linked to Climate Change
If it feels like allergy season is lasting longer, you’re not alone. A new analysis from Climate Central reveals that the freeze-free growing season has lengthened in 87% of U.S. Cities since 1970, giving plants about three extra weeks each year to grow and produce pollen. Climate Central attributes this trend to rising temperatures driven by the burning of fossil fuels.
Growing Season Expansion and Regional Impacts
The most significant increases in the growing season are occurring in the Northwest. This extended growing period directly correlates with increased pollen production, potentially worsening allergy symptoms for the roughly one in four adults in the U.S. Who suffer from seasonal allergies.
Seattle Area Experiences Notable Changes
In the Seattle-Tacoma area, the growing season has increased by approximately 12 days over the past 50+ years. Local allergy specialists at Optum Care Washington have observed this trend over the last decade. While the 2026 allergy season started earlier than usual due to a milder and drier winter, pollen levels haven’t yet surpassed those of 2025, according to data from the Northwest Asthma and Allergy Center. Still, grasses and weeds, which typically trigger later-season allergies, are expected to emerge.
Warming Trends Across the U.S.
Climate Central’s analysis, based on data from the National Oceanic and Atmospheric Administration (NOAA), shows that 98% of 241 major U.S. Cities have experienced warmer spring temperatures since 1970, with an average increase of 2.6°F. Human-caused climate change is responsible for at least half of this warming, and in 69% of cities, it explains all of the observed temperature increase.
Nationally, 240 of 242 U.S. Cities analyzed have warmed since 1970, with an average temperature increase of 2.9°F. 98% of 244 U.S. Cities have seen average winter temperatures rise from 1970 to 2025, increasing by nearly 4°F on average.
Fastest-Warming Cities
The cities experiencing the most rapid warming include Reno, Nevada; Las Vegas, Nevada; El Paso, Texas; Tyler, Texas; and Burlington, Vermont. The fastest-warming states are Alaska, Delaware, Massachusetts, and New Jersey.
Source: Information in this story comes from original reporting by FOX 13 Meteorologist Abby Acone, Climate Central and Northwest Asthma and Allergy Center.