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Minnesota is now in peak tree pollen season. If you feel like your allergies have gotten worse in recent years, you are not alone. 

Studies have linked warming temperatures to longer and more intense pollen seasons in the U.S.

higher concentrations of carbon dioxide have also been found to lead to more pollen production

Indeed, according to a quick analysis of local data, higher temperatures in March and April do correlate with the tree pollen season starting sooner right here in Minnesota.  

Between 1993 and 2020, the years for which data is available, the earliest the tree pollen season began was March 12. That was in 2016 when the average low temperature in March and April was 36 degrees — around five degrees above average.  

The latest date a tree pollen season started was nearly seven weeks later on April 29. The average low temperature in March and April that year, 2013, was around 26 degrees — about five degrees below average.   

graph of temperatures and season start date

Making matters worse for allergy sufferers, at least according to national studies, pollen season is both starting earlier and lasting longer. Locally, average low temperatures in March and April increased by around three degrees from 1993 to 2020. 

While the length of the tree pollen season varied considerably over that same period, from 28 days in 2018 to 113 days in 2011, the overall trajectory according to our analysis was an increase of five days over the 26 years. 

graph of tree pollen season length by year

Notably, the earlier onset of warmer temperatures isn’t the only factor affecting plant growth and pollen season length. Precipitation as well as temperature changes after pollen season begins can also impact the season’s length. 

Local tree pollen data has not been available for the past few years, according to reporting from 

. Pollen forecasts available through many weather apps are modeled from weather and climate data. 

But we do know that, so far, this spring is off to a relatively warm start, with an average daily low temperature in March and April of 34 degrees (three degrees above the recent average).  

Looking at years with similar average low temperatures in the past, we might predict that tree pollen season started sometime during the first couple weeks of April. 

Unfortunately for allergy sufferers, it will probably continue for at least a couple more weeks. The earliest that tree pollen season has ended in the past quarter-century was May 14 in 1998. That year, grass pollen season started one week later.   

Influenza drops decisively, RSV remains low 

Influenza hospitalizations in Minnesota dropped again in the most recent weeks’ worth of data, closing any suspicions that the state’s lingering flu season might never come to an end. 

The Minnesota Department of Health’s latest data show that hospital admission rates due to the flu are not as low as they are for respiratory syncytial virus, but they appear headed in that direction. 

graph of hospitalization rates from respiratory viruses in MN

U.S. COVID-19 Hospitalizations reach lowest numbers since pandemic’s start 

The Center for Infectious Disease Research and Policy’s 

 reports that U.S. hospitalizations for COVID-19 are now at the lowest point in the pandemic, even lower than last summer. 

The Centers for Disease Control and Prevention (CDC) is no longer requiring hospitals to report COVID-19 admissions as of May 1.  

US and Minnesota COVID hospitalization rates

Ending the reporting requirement may further cloud our ability to detect possible future changes in COVID-19 activity. For example, new COVID-19 variants are once again on the rise, with the recently dominant JN.1 

now giving way to so-called “FLiRT” variants

It is unclear whether these newer strains, 

which the CDC now estimates as comprising one-third of the COVID-19 in circulation nationally

, will result in an uptick in hospitalizations. But the new reporting rule will make it more difficult to tell.  

We asked officials at the Minnesota Department of Health whether that change would impact COVID tracking here, and they indicated “we will continue to receive and report the information 

 related to [COVID-19] Hospitalization Trends, Hospitalization Rate by County of Residence, and Demographics (Age Groups, Sex, Race/Ethnicity). 

What will discontinue is data on hospital capacity (currently COVID-19 and Non-COVID-19 Hospitalizations, Overall Beds Available and Beds Available Over Time).” 

Wastewater monitoring remains another important source of COVID-19 monitoring, and the latest data out of 

the University of Minnesota’s on-going Wastewater Surveillance Study

 shows more good news: COVID-19 levels are down statewide over the most recent week, including drops in all seven of the study’s regions.  

Measles: Continued global and U.S. spread, but nothing new here in Minnesota 

The Minnesota Department of Health has not reported any new cases of measles in the state since 

the third case this year was reported back in February

 of the highly infectious disease over the past two weeks, bringing the yearly total to 128. This already makes 2024 the highest year of U.S. measles infection since 2019, when 1,274 cases were identified over the whole year.  

, measles cases are up worldwide, “from more than 170,000 cases in 2022 to more than 320,000 cases in 2023, according to WHO’s [the World Health Organization’s] count.” Through November 2023, the lasted data reported by WHO, 

51 countries were reporting officially defined “large or disruptive” measles outbreaks

, roughly triple the number of countries reporting such outbreaks in 2020, and about double the number of nations reporting such outbreaks through most of 2021. 

Elisabeth Gawthrop

Author

Craig Helmstetter

Minnesota is now in peak tree pollen season. Studies have linked warming temperatures to longer and more intense pollen seasons in the U.S.

Allergies and climate: Pollen in Minnesota comes earlier with warmer temperatures

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