Ah, spring. Even after a moderate winter, warm days and blooming daffodils cannot come soon enough. In fact, spring weather is arriving sooner than usual, especially in the northern United States and Canada, according to studies that track weather and plant blooming patterns.

In the Midwest, trees leaf out and lilacs and honeysuckle flower sooner with the early onset of pleasant spring temperatures.  

 But early spring has a troublesome side effect: premature allergy season, which plagues sufferers with itchy, watery eyes, drippy noses, sneezing and wheezing.  Scientists predict that as carbon dioxide levels in the atmosphere continue to rise, seasonal allergies will start sooner, be more intense, and last longer into fall.  

The effect is a consequence of climate change, also known as global warming.

“With climate change and carbon dioxide, we see a connection for earlier springs and later falls,” says Lewis Ziska, Ph.D., a plant physiologist (or “weed scientist”) with the United States Department of Agriculture Agriculture Research Service.  

These seasonal shifts cause some plants to produce more pollen, particularly ragweed in the fall, explains Dr. Ziska, and the “allergenicity” or potency of the pollen has increased.  First frosts are happening later in autumn, he adds, extending allergy exposure times.  

It all adds up to the potential for longer and more intense allergy seasons, a trend confirmed by local allergists.  

“I am seeing people sooner, complaining that their allergy and asthma symptoms were starting early,” says Jyothi Tirumalasetty, M.D., an allergy and immunology specialist at the University of Illinois at Chicago.  

Dr. Tirumalasetty observed that allergy season lasted longer than usual last fall, and she has seen the early arrival of spring allergy symptoms over the past several years.  

“We used to advise patients to start taking their medications at the end of March, to get ready for allergy season,” she says, “but now we tell them to start at the end of February.”

Airborne plant pollens and mold trigger seasonal allergies, also called “allergic rhinitis” or hay fever – which has nothing to do with hay and is not accompanied by a fever, notes Paul A. Greenberger, M.D., a professor of medicine in the Division of Allergy and Immunology at Northwestern’s Feinberg School of Medicine.  

Dr. Greenberger explains that tree pollen is released in about mid-March, followed by grass pollen in mid-May, and then ragweed pollen starting mid-August through September.  Outdoor mold spores release from April until the first hard autumn freeze. In May, grass pollen overlaps with mold spores and tree pollen, delivering a multi-layered allergen hit that Dr. Greenberger calls the “triple whammy.”

But typical pollen seasons are now in flux, say various environmental studies, including one led by Dr. Ziska that found a lengthening of autumn’s ragweed pollen season since 1995.  

The study tracked the date of first frost, which kills off pollen-producing plants and effectively ends allergy season in the fall.  

In 10 cities from Texas and Oklahoma through several midwestern states and into Canada, the study found that first frosts were delayed by anywhere from one day in Georgetown, Tex., to 13 days in Madison, Wis., to almost four weeks in Saskatoon, Saskatchewan – the most northerly city in the study.  

According to the Environmental Protection Agency, first frost delays align with patterns of increased warming at higher latitudes, toward both poles.  

Dr. Ziska’s study, which appeared in the Proceedings of the National Academy of Sciences, concludes that “if similar warming trends accompany long-term climate change, greater exposure times to seasonal allergens may occur with subsequent effects on public health.”  

For example, longer pollen seasons may increase allergic sensitivity, as well as the duration and severity of the symptoms of allergic rhinitis and asthma – chronic health issues that already cost an estimated $21 billion per year in the United States, the study reports.

Asthma affects more than seven million children and 17 million adults in the United States, while more than 50 million Americans suffer from seasonal allergies each year, according to the American College of Allergy, Asthma and Immunology. Locally, Chicago was declared the sixth “sneeziest and wheeziest” city and the ninth most dangerous “asthma capital” in the U.S., according to the National Resources Defense Council’s (NRDC) 2015 allergy report.  

The ranking is based on the number of hot sunny days when ragweed and excess ground-level pollution, also known as “ozone smog,” overlap – a combination harmful to respiratory health and one that often drives asthma sufferers to hospital emergency rooms.

The NRDC report states that “the severity of both allergies and asthma is closely linked to environmental conditions, particularly air quality,” and intense ragweed-ozone conditions provide “evidence of the urgent need for taking action now to reduce the health threats posed by climate change.”  

The report advises that minimizing emissions from ozone-producing sources such as industrial facilities, electric power plants, and motor vehicles “can help reduce ozone air pollution and climate change, helping to create better air quality conditions.”