March 24 (UPI) -- Rising temperatures from climate change are causing the spring allergy season to start earlier and last longer in many regions of North America, a report released Wednesday by environmental research organization Climate Central found.
Climate Central is a non-profit news organization composed up of scientists and journalists who conduct scientific research and report on issues related to climate change and its impact on the public.
Over the past 50 years, the spring growing season increased in length in 166, or 82%, of more than 200 locations throughout North America that the group assessed, the data showed.
The season was extended by at least four weeks in 38 of those areas, with Bend, Ore. and Reno, Nev., leading with 99 additional growing season days.
The findings mean that in many parts of the United States and Canada, people with pollen allergies are exposed to the airborne irritant for longer periods, according to Climate Central.
"Many people may experience allergies as a minor inconvenience, but seasonal allergies can have serious consequences and decreased quality of life for those with respiratory problems like asthma," the organization said in its report.
More than 25 million people in the United States have seasonal pollen allergies, according to the Centers for Disease Control and Prevention.
Of the 25 million people nationally with asthma, 60% have allergic asthma, meaning that exposure to pollen can trigger their attacks of severe shortness of breath, the agency reports.
Pollen is a powdery substance made up of tiny grains produced by trees, flowers, grasses and weeds to fertilize other plants of the same species.
It is particularly prevalent in the spring across the United States, when many plants begin to grow after the winter months.
The earlier onset of spring in some parts of the country, due at least in part to warming caused by climate change, has led to an increase in asthma- and allergy-related hospitalizations, according to an analysis published last summer by JAMA.
For their report, Climate Central researchers analyzed the length of the spring growing season, or the number of days between the last spring freeze and first fall freeze, over a 50-year period in 203 locations across North America.
Locations were only included in the analysis if they had a "freeze season" of at least 90 days with a temperature minimum lower than or equal to 32 degrees.
In many regions included in the analysis, the length of the spring growing season -- and the allergy season -- grew by 20 days or more between 1970 and last year.
Although it increased by 11 days in Boston and 13 days in Chicago over that period, it grew by 17 days in Dallas-Fort Worth and by 32 days in Cleveland, Minneapolis-St. Paul and Philadelphia.
The spring season in New York City increased by 26 days over the 50-year period, according to the researchers.
"With a longer pollen season and high pollen concentrations, asthma and allergy reactions can become even more severe and expensive to treat, and unfortunately this burden is placed on the most vulnerable populations," the Climate Central researchers said in their report.