(CNN)Allergies aren't just a sneezy seasonal annoyance.
Hay fever has major health and economic consequences. It exacerbates asthma and weakens defenses against respiratory viruses, resulting in more emergency room visits and disrupted schooling and work.
Climate change has already made pollen seasons in the United States and Canada worse, a new study of almost three decades' worth of data has revealed. The pollen seasons are getting longer and more intense.
The amount of time people in North America are exposed to pollen as well as the amount of pollen had "increased significantly" in recent decades, according to the authors.
The researchers looked at different pollen metrics between 1990 and 2018 from 60 monitoring stations across North America. Pollen seasons were starting up to 20 days earlier and lasting for up to eight days longer, the scientists found.
There was also an increase in the pollen count or concentration of pollen, with a rise of 20.9% between 1990 and 2018 -- and a 21.5% increase for the spring season alone.
"There's an enormous body of research on how climate change is already affecting our health. Our study fills in a key piece connecting climate change to pollen, which is one of the largest drivers of asthma, allergies, and respiratory health problems," said William Anderegg, an assistant professor of biology at The University of Utah and lead author of the study that published in the journal PNAS on Monday.
"It's a clear example that climate change is here and now."
The largest and most consistent increases were in Texas and the midwestern United States, the study found -- something that surprised Anderegg. He had expected to see larger pollen increase in more northern states.