Of the many disasters caused by climate change worldwide, scientists have now identified a more personal one: it makes allergy season worse.

That’s the message of a new study in the Proceedings of the National Academy of Sciences, published on Monday. The researchers found a strong link between the warming of the planet and the pollen season that will make many of us just a little more fearful of spring.

According to the new paper, the combination of warming air and higher levels of carbon dioxide in the atmosphere has resulted in North American pollen seasons starting about 20 days earlier on average since 1990 and having 21 percent more pollen.

Scientists have been suggesting for some time that the season of the year is getting longer and more terrible, and new research is providing more detailed and estimates of how much a warming planet is responsible for greater misery. They concluded that climate change was causing about half the trend in the pollen season and 8 percent the higher pollen count. In addition, the trend towards higher pollen counts is accelerating, according to the researchers.

The greatest effects were seen in Texas, the Midwest, and the Southeast, said William Anderegg, assistant professor of biology at the University of Utah and lead author of the new study. The effects were less apparent in the northern United States, including New England and the Great Lakes states. The biggest pollen surge came from trees as opposed to grasses and weeds, he said.

Researchers used the techniques of attribution science commonly used to determine how far extreme weather events such as heat waves, forest fires, or the amount of rain a hurricane brings are worse than in a world without climate change.

Applying this branch of science to pollen was a novel and welcome idea, said Kristie Ebi, a professor at the University of Washington’s Center for Health and Global Environment who was not involved in the study. “It’s a great job,” she said. “There is very little research into the application of recognition and attribution analysis to the health risks of a changing climate.”

The researchers examined data collected from 60 long-term pollen monitoring stations across the American continent and compared the results with various climate models to find correlations. They also tried to rule out potentially confusing factors by using satellite photos to determine whether changes in land use or tree growth during the study period near the pollen monitoring stations skewed the results.

“The world is a chaotic place,” said Dr. Anderegg with many potentially confusing influences, “but the really strong signal here and the attribution to climate change are convincing.”

The paper concluded that “A clearly identifiable and relatable fingerprint of man-made climate on pollen count in North America is a powerful example of how climate change is contributing to adverse health effects by worsening the pollen season”.

Allergies aren’t just a case of runny nose, of course: they have serious public health implications, including asthma and other respiratory diseases. Studies have shown that students do less well in school during the high season of pollen and that periods of pollen have been linked to a higher susceptibility to respiratory viruses – a threatening finding during the coronavirus pandemic.

Asthma: “It’s not a simple allergy, it’s a life-threatening condition,” said Amir Sapkota, professor in the University of Maryland’s School of Public Health. His research suggests that early onset of the pollen season correlates with a higher risk of hospitalization for asthma. In addition, the effects of asthma are felt unevenly as vulnerable populations are at greater risk of developing serious illnesses due to inadequate access to health care and the means to purchase medicines.

Dr. Ebi of the University of Washington cited figures from the Centers for Disease Control and Prevention that 24.8 million people in the US had asthma and 19 million adults said they had hay fever in the past 12 months. Seven million children had respiratory allergies in the same period. The direct cost of childhood asthma alone was calculated to be US $ 5.9 billion in 2013, the latest figure reported in a 2019 study.

“This study shows that climate change is now and could affect the health of people with allergies or asthma,” Pollen said.

Dr. Anderegg suggested that more research on the effects of pollen should begin with greater monitoring and measurement of pollen levels. There are far fewer pollen monitoring stations than those that measure particulate matter and air quality. “We really don’t monitor pollen as an air pollutant,” he said.

The prospects, he said, were not happy. “We expect this to worsen over the next few decades.”

Dr. Anderegg added that the research also has a personal meaning. “I have to take allergy medication eight months out of the year,” he said, “and there are still times when I am still unhappy during the pollen season.”