How Climate Change Is Making Allergy Season Worse

Warmer weather means more pollen and longer pollen seasons.

Catkins on Paper Birch Tree
The greatest increases were found in tree pollen. skhoward / Getty Images

Climate change can be blamed for warming oceans and shrinking animal habitats. But in a less-expected consequence, warming temperatures have made allergy seasons worse, new research suggests. 

Over the last three decades, pollen seasons have changed to start about 20 days earlier, last about 10 days longer, and feature an increase of 21% more pollen, according to a study published in the Proceedings of the National Academy of Sciences.

“Human-caused climate change was the dominant driver of pollen season start date and length,” study lead author William Anderegg, an assistant professor of biology at the University of Utah, in Salt Lake City, tells Treehugger.

“The strong link between warmer weather and pollen seasons provides a crystal-clear example of how climate change is already affecting peoples' health across the U.S.”

For the study, Anderegg and his fellow researchers collected measurements from 60 pollen count stations across the U.S. and Canada between 1990 and 2018. The stations are maintained by the U.S. National Allergy Bureau.

They found increases in pollen concentrations and the length of pollen seasons. Specifically, pollen counts increased by about 21% over the three decades. The greatest increases were noted in the Midwestern U.S. and in Texas, and more changes were found in tree pollen than in other plants.

Because pollen seasons now start about 20 days earlier than in 1990, the researcher say this suggests that warming is causing the plants’ internal timing to begin making pollen earlier in the year.

Finding the Link

Researchers compared the information they collected to nearly two dozen climate models.

They concluded from their findings that climate change accounts for about half of the extended pollen season and around 8% of the overall increase in pollen concentrations.

“We used a cutting-edge set of scientific tools called ‘detection and attribution,’ whose goal is to directly estimate how much climate change is playing a role in a given change,” Anderegg explains. “There are certainly other potential drivers, but we were very careful and thorough to account for potential confounding factors and isolate the effect of climate change directly with this technique.”

This isn't the first time that researchers have explored the link between climate change and its impact on pollen and allergies. Some earlier, smaller studies found links between temperature and pollen. But usually these were performed in greenhouses or only on small plants.

This is the first time that the link has been explicitly made to climate change and done across the U.S. and Canada, Anderegg says.

"Climate change isn't something far away and in the future. It's already here in every spring breath we take and increasing human misery," says Anderegg. "The biggest question is, are we up to the challenge of tackling it?"

View Article Sources
  1. Anderegg, William R. L., et al. "Anthropogenic Climate Change is Worsening North American Pollen Seasons." Proceedings of the National Academy of Sciences, vol. 118, no. 7, 2021, p. e2013284118, doi:10.1073/pnas.2013284118

  2. Müller, Florian, and Ivo Rieu. "Acclimation to High Temperature During Pollen Development." Plant Reproduction, vol. 29, no. 1-2, 2016, pp. 107-118, doi:10.1007/s00497-016-0282-x