Allergy season is getting longer in Wisconsin, and climate change is to blame

• Climate change is causing an earlier start to spring and a later end to fall in Wisconsin. That creates a longer "growing season" for trees and plants to give off pollen.
• An analysis by Climate Central, a nonprofit that reports on climate science, found the growing season has gotten 25 days longer in Milwaukee and 33 days longer in Madison since 1970.
• Allergists at two of Wisconsin's pollen-counting stations say they've also seen a longer season, and it's driving demand among their patients for more treatment.

Tough news for those who sneeze and sniffle at certain times of year: allergy season in Wisconsin is getting longer, and climate change is to blame.

An analysis this month from Climate Central, a nonprofit organization that reports on climate science, found that the number of days per year without frost increased in more than 170 American cities since 1970, including several in Wisconsin. An earlier start to spring and a later freeze in the fall mean trees and plants that produce pollen have more time to do so.

That's reflected in data from Wisconsin's pollen-counting stations in Milwaukee and Madison, where allergists say the season lasts as much as 50% longer than it did in the past — and pollen concentrations are higher, too.

"We've known that when you grow plants in higher temperatures, they'll produce more pollen per plant, for longer. We've known that this is coming," said Dr. Gary Steven, a community allergist at the Allergy, Asthma & Sinus Center in Greenfield. "But now ... it's actually going on."

How does climate change affect allergies?

About a quarter of U.S. adults and 19% of children have seasonal allergies, which are caused by their immune systems overreacting to outdoor stimulants like pollen from trees, grass and weeds.

Trees, which are first to produce pollen each year, start to pollinate when temperatures begin to warm up. Ragweed, one of the last plants to pollinate, stops producing pollen with the first frost of the year. The period between the year's first and last frost is referred to as the growing season.

In Wisconsin, climate change is causing spring to arrive earlier and the first fall freeze to happen later than it did in 1950, according to the Wisconsin Initiative on Climate Change Impacts. The Climate Central analysis found that the growing season in Madison has increased by 33 days since 1970, and by 25 days in Milwaukee. It's also gotten longer in Green Bay, Wausau, La Crosse and Eau Claire.

In addition to a longer growing season, there's also more carbon dioxide in the atmosphere, said Dr. Andrew Rorie, a professor of allergy and immunology at the University of Nebraska Medical Center. That's driven largely by human activities, like burning fossil fuels.

More atmospheric carbon dioxide, which plants use to make energy, means more plant food, Rorie said. "These plants are happy and making more pollen, and they're pollinating longer."

One study of ragweed has even shown that more atmospheric carbon dioxide makes the plant's pollen grains bigger and more allergenic.

What do pollen trends from Milwaukee, Madison show?

UW-Madison has been counting pollen for more than 30 years, said Dr. Mark Moss, an allergist at UW Health. In the past, the spring tree pollen season would begin at the start of April, Moss said. Today, it's much more likely to appear in March — and last year, following Wisconsin's warmest winter on record, the station measured pollen at the end of February.

"In a normal year, I tell my patients they should start their allergy medications around St. Patrick's Day," he said. "But last year, that would have been too late."

This year, Moss said the station started measuring pollen from cedar, elm and maple trees in mid-March at significant levels.

The end of ragweed season would fall around the end of October decades ago, he said, but today, it frequently pushes into the first or even second week of November.

Milwaukee may get a bit of relief because of its border with Lake Michigan, which obviously isn't home to any trees or plants that produce pollen. But that relief goes away quickly as you head inland, Moss said.

In the Milwaukee area, Steven's pollen-counting data stretches back to the early 2000s. He said he's seen about a 30% increase in the length of the tree pollen season on average — from roughly 80 to 104 days — since then. One other factor besides climate change that could be playing a role is an increase in privet, an invasive tree species that pollinates late in the year. But even accounting for privet, Steven said, the length of tree pollen season is still on the rise.

The pollen counts themselves are also so much higher today than what he saw 20 to 30 years ago that he only uses 10-year averages to understand the severity of the season.

"If I were to use all of the data in calculating severity, we would always be in the high range," Steven said.

Both doctors are seeing these changes reflected in their own patients. Steven has seen an increase in people wanting to continue allergy shots because their symptoms have continued despite targeted treatment in recent years. In Madison, the number of allergists at the university is growing because there's been so much demand for treatment, Moss said.

How can I keep my allergies under control?

Even as allergy season gets longer and more severe, doctors who treat allergies will still be able to use "tried and true" methods to help people get relief, Rorie said.

If you're allergic to pollen, keep your windows closed, and take a shower and change clothes after you've been outside, he said. Over-the-counter medications like Claritin, Zyrtec and Allegra can help keep symptoms at bay. If they're not doing enough, consider making an appointment with an allergist to identify what exactly you're allergic to and try prescription medication, immunotherapy or allergy shots.

To view current pollen counts at stations in Milwaukee, Madison and La Crosse, visit pollen.aaaai.org.

Madeline Heim is a Report for America corps reporter who writes about environmental issues in the Mississippi River watershed and across Wisconsin. Contact her at 920-996-7266 or mheim@gannett.com.