In recent years, seasonal allergies, also called ha y fever or allergic rhinitis（过敏性鼻炎）,have been hitting people around the world especially hard. Seasonal allergies cause great trouble to people, such as sneezing, tiredness, a runny nose or a congested nose which makes it hard for people to breathe.
In 2021, as many as 81 million Americans experienced seasonal allergies, according to the Asthma and Allergy Foundation of America. The main cause for seasonal allergies is the spread of pollen（花粉）, and researchers are blaming climate change for it.
As the planet warms, scientists are seeing two main changes to allergy seasons. Allergy season length is longer and pollen levels are increasing. With warmer winter temperatures, the frost-free season starts earlier in the spring and ends later in the fall. In a research done by William Anderegg, an associate professor at the University of Utah, US, he saw pollen seasons starting about 20 days earlier this year than they did in the 1990s.
Pollen levels have also been increasing in the US. Anderegg's research found about a 21percent increase in the amount of pollen in the air from 1990 to 2018.
This increase is likely fueled by a combination of higher temperatures and higher carbon dioxide levels in the air, according to Anderegg. The burning of fossil fuels ——a primary cause of global warming — increases carbon dioxide. As CO2 levels go up, plants and trees produce more pollen, according to NBC.
Increased rainfall brought on by global warming may be making allergies worse too. "Thunderstorms, pressure changes, and humidity changes that we see through climate change break down pollen spores（孢子） into even smaller pieces, and these pollen spores can then more easily enter the lungs," Brooke Lappe, a doctoral student at Emory University's Rollins School of Public Health, said to NBC.
