Hay fever is one of the most common allergies in the United States, and scientists believe global warming is the reason why so many people are experiencing worsening symptoms.
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Itching, sneezing, and watery eyes are all things you're familiar with if you struggle with seasonal allergies. While these cold-like symptoms are triggered by outdoor and indoor allergens—think pollen and dust mites—that are typically more rampant during spring, a new study suggests that climate change has lengthened hay fever season. The research, which was published in Proceedings of the National Academy of Sciences, reveals that global warming is causing extra weeks of seasonal allergies.

To obtain their findings, the researchers analyzed measurements of airborne pollen and mold across the United States and Canada between 1990 and 2018 as documented by the National Allergy Bureau. The measurements were collected between those years and hand-counted by staff at 60 stations across both countries. According to the study, nationwide pollen quantities skyrocketed by 21 percent over the 28-year period. The most notable increases were recorded in Texas and the Midwestern U.S. "The strong link between warmer weather and pollen seasons provides a crystal clear example of how climate change is already affecting people's health," says the study's lead author, Dr. William Anderegg of the University of Utah, in a statement.

person outdoors sneezing into tissue
Credit: raquel arocena torres / Getty Images

Greenhouse gas experiments have shown that an increase in temperature and atmospheric carbon dioxide can cause more pollen production. Traditionally, pollen season spanned just over a month—from mid-June to mid-July—but the study finds that it now begins about 20 days earlier than in 1990, lasting from March until September. Scientists believe climate change is to blame as warmer temperatures cause the internal timing of plants to start producing pollen earlier in the year.

Nearly two dozen climate models have shown that global warming accounts for about half the lengthening of hay fever season. The research also reveals that climate change's contribution to pollen season is only accelerating—right now it's responsible for roughly eight percent of the increasing pollen. "Climate change is not something far away and in the future," says Dr. Anderegg. "It is already here in every spring breath we take and increasing human misery. The biggest question is—are we up to the challenge of tackling it?"

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