Climate MattersApril 6, 2022

Pollen Season & Climate Change


  • Pollen season is here, and climate change is making it worse. Warming contributes to longer pollen seasons, and higher carbon dioxide levels can increase pollen production.

  • The length of the growing season (and the pollen season) has increased since 1970 in 85% of the 203 U.S. locations Climate Central analyzed.

  • A new study suggests that pollen concentrations in the U.S. could increase 200% with high future rates of carbon dioxide emissions.

  • The health burdens of worse pollen seasons could be higher on low-income and minority populations that have disproportionate rates of respiratory illness like asthma.

Longer U.S. Growing Season - Pollen Season & Climate Change
Longer U.S. Growing Season
Longer Local Growing Season - Pollen Season & Climate Change
Longer Local Growing Season

Longer growing season = longer pollen season

With the arrival of spring comes pollen and seasonal allergies for millions of Americans. And climate change is only making matters worse with longer and more intense pollen seasons.

Research suggests that human-caused warming was a primary driver of longer pollen seasons (about 20 days longer on average) across North America from 1990 to 2018.

Spring-like temperatures now arrive earlier in the year, and summer temperatures linger later—meaning that the growing season (the time between the last spring freeze and first fall freeze) is getting longer.

Longer growing seasons mean longer pollen seasons and more respiratory health burdens for millions of people with seasonal allergies.

Longer growing seasons across the U.S.

Climate Central analyzed the change in growing season length for 203 U.S. locations and found that:

  • The growing season has gotten longer since 1970 in  85% (172 of 203) of locations analyzed.

  • The average change across all 203 locations was an increase of 16 days. 

  • In 38 places, the growing season lengthened by at least four weeks. 

  • Bend, Ore. saw the greatest increase with 101 additional growing season days since 1970.

More CO2 emissions = more pollen production

Climate change makes pollen seasons not only longer—but also more intense. Higher carbon dioxide levels in the atmosphere can boost plant growth and lead to more pollen production in grasses and ragweed.

And with continued high rates of carbon dioxide emissions, the U.S. could face up to a 200% increase in pollen production by the end of the century, according to a recent study.

Different types of plants produce pollen at different times of year and grow in different parts of the country—as shown in this video from researchers at the University of Michigan.

As research progresses, so will our ability to predict when and where pollen season changes will occur, which can help people prepare for and manage the health effects.

Impacts of longer, more intense pollen season

Many people may experience allergies as a minor inconvenience, but longer and more intense pollen seasons can have serious consequences for those with respiratory illnesses like asthma.

About 60% of the 25 million Americans with asthma have allergic asthma一where pollen can trigger an asthmatic attack. With longer and more intense pollen seasons, asthma and allergy reactions can become even more severe and expensive to treat.

Effective medications and therapy to manage symptoms can be a burden on lower-income families, especially since asthma is more prevalent in families living below the poverty line.

And the highest asthma diagnoses, hospitalizations, and deaths are disproportionately found in racial and ethnic minority populations due to a range of factors including access to health care and discriminatory housing policies.


What are pollen concentrations like in your area? Which plant species are producing the pollen?
Nearly 25 million people in the U.S. are estimated to have asthma, and research suggests that climate change might already be contributing to longer pollen seasons and increased pollen concentrations. You can search for local pollen counts and sign up for pollen level alerts through the American Academy of Allergy, Asthma, and Immunology. You can also use the Allergy and Botany Research Library to discover which plant species contribute to pollen reactions in your area.

Are you located in an allergy capital?
The severity of the allergy season varies across the country. The Asthma and Allergy Foundation of America conducted a 2022 report on the top 100 Allergy Capitals in the U.S., ranking cities on spring and fall pollen scores, over-the-counter medicine use, and the availability of board-certified allergists/immunologists. Check out where your city placed on the worst allergy capital list.

How are certain racial and ethnic groups in my area disproportionately affected by a longer allergy season?
Check out the AAFA’s recent report on Asthma Disparities in the U.S. You can also look at specific infographics and statistics on Black, Hispanic, and Indigenous American populations.


The SciLine service, 500 Women Scientists or the press offices of local universities may be able to connect you with local scientists who have expertise on the extended pollen and allergy season in your area. The American Association of State Climatologists is a professional scientific organization composed of all 50 state climatologists.

In addition, the American Academy of Allergy, Asthma, & Immunology has a directory of allergists and immunologists across the country. Other health professionals and experts can be found on The Medical Society Consortium on Climate and Health.



Daily minimum temperature data from 1970-2021 was obtained from the Applied Climate Information System. The length of the growing season is the number of days between the last spring freeze and first fall freeze. Locations were only included in the analysis if they had an average “freeze season” of at least 90 days with a minimum temperature less than or equal to 32°F. Additionally, Wheeling, W. Va was removed from any summary statistics due to large data gaps in its period of record. As a result, 203 stations were included in this analysis.