New research suggests that as climate change continues to push temperatures higher, pollen season will continue to get longer and more intense, potentially causing it to "start up to 40 days earlier and last up to 19 days longer than it does today," Yingxiao Zhang and Allison Steiner, both atmospheric scientists at the University of Michigan, write for The Atlantic.

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The United States could see a 200% increase in total pollen

In Zhang and Steiner's latest study, published last week in Nature, they explain how the United States' total pollen will increase by up to 200% this century if the world maintains its current carbon-dioxide emissions. "Under that scenario, the spring pollen season will generally start up to 40 days earlier and last up to 19 days longer than it does today," they write.

For the study, they created a model using more than a dozen types of grasses and trees, as well as 15 different types of pollen, to determine how pollen would impact regions across the United States in different ways.

Ultimately, they found the Northeast will experience the largest pollen increase because of species such as oak and cypress. However, they found that allergens will rise "just about everywhere, with consequences for human health and the economy."

To predict when pollen waves are coming, Zhang and Steiner are working on adapting the model from their study to create more accurate local pollen forecasts. "Most pollen forecasts right now provide only a very broad estimate," they write. "Part of the problem is that there aren't many observing stations for pollen counts: Fewer than 100 of these stations are distributed across the country. Michigan, where we live, doesn't have any."

Notably, they explain that the process used to measure various types of pollen is very labor intensive. As a result, current forecasts are largely based on what a single station has observed in the past and the weather forecast—resulting in a lot of uncertainties.

In comparison, according to Zhang and Steiner, their "model, if integrated into a forecasting framework, could provide more targeted pollen forecasts across the country."

Specifically, their model would enable them to not only estimate "where trees are from satellite data and on-the-ground surveys," but also determine "how temperature influences when pollen is released—what we call its phenology." Then, they write that they could use that information in combination with "meteorological factors such as wind, relative humidity, and precipitation to figure out how much pollen gets into the air, and atmospheric models can show how it is blown around, to create a real-time forecast."

In turn, that information would allow them to look at where pollen might be in space and time, providing people with allergies a forecast for pollen levels.

However, there are some uncertainties surrounding long-term pollen projections, they write. For instance, scientists still don't totally understand why plants can produce different levels of pollen from year-to-year. "There's not a good way to include that variability in models," Zhang and Steiner write. "Also unclear is how plants will respond if carbon-dioxide levels go through the roof."

Notably, a 2021 study found that the North American pollen season was already around 20 days longer than it had been in 1990, with pollen concentration up by about 21% overall.

"Increased pollen levels will have a much broader impact than a few sniffles and headaches," Zhang and Steiner write. Currently, seasonal allergies impact roughly 30% of the U.S. population, resulting in economic impacts, including higher health care costs and more missed workdays.

"In the coming years, those impacts will only intensify," they add. (Zhang/Steiner, The Atlantic, 3/20)