POLLEN PROBLEMS: Climate Change, the Growing Season, and America’s Allergies

https://www.climatecentral.org/news/report-pollen-allergies-climate-change

Mar. 27, 2019

Nearly 20 million Americans suffer from pollen allergies. Analysis of local temperature data by Climate Central and recent scientific research show that climate change is prolonging their season of suffering.

Global warming is extending the freeze-free season, giving plants more time to grow, flower, and produce pollen. And as atmospheric carbon dioxide (CO2) levels rise, laboratory experiments suggest, some plants that produce allergenic pollen produce even more of it.

These trends will worsen as humanity dumps more carbon into the atmosphere. Like global warming’s effects on heat waves and vector-borne diseases, climate change’s consequences for pollen allergies reveal how greenhouse gas emissions are already damaging Americans’ health.

Over the past few decades, the prevalence of allergies among Americans has skyrocketed. In 1970, about one in ten Americans suffered from hay fever, which is caused by airborne allergens, such as pollen and mold spores; by 2000, three in ten did.

Asthma—which often occurs alongside pollen allergies—has become more common, too. The proportion of Americans who suffer from asthma rose from 3.1 percent to 8.4 percent of the population between 1980 and 2010. Rates are even higher among African-Americans, low-income households, and children. Today, some 6.2 million Americans under the age of 18 suffer from the chronic disease.

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Researchers do not fully understand the causes of the upward trend in allergies. But one thing is clear: as humans warm the atmosphere, the freeze-free season generally begins earlier and lasts longer each year, extending the time during which plants can grow and produce pollen.

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To understand how the growing season has changed across the United States, Climate Central assessed temperature data for 201 cities. Of those cities, 83% saw their freeze-free seasons lengthen since 1970. In the average city, the amount of time between the last and first freeze of the year grew by just over two weeks.

In 34 cities, including El Paso, Minneapolis, and Philadelphia, the season between first and last freeze grew by at least four weeks. In Bend, Oregon; Medford, Oregon; and Las Cruces, New Mexico, it lengthened by at least two months—among the biggest increases in the country. In general, relative to early twentieth-century averages, the freeze-free season has lengthened the most in the western United States, becoming about 19 days longer in the Southwest and 16 days longer in the Northwest. And as the frost-free season has lengthened, so has the pollen season of ragweed, one of the most commonly allergenic plants in the United States. In parts of the upper Midwest, for instance, the ragweed pollen season lengthened by about three weeks between 1995 and 2011.

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