Ragweed, Ambrosia trifida and A artemisiifolia, are annual plants native to the Midwestern US and significant sources of airborne allergenic pollen. We use 20 years of data to test the hypothesis that warming climate would result in a longer pollenating season for this common allergenic plant.
Pollen was collected atop a 6 story building in downtown Kansas City, Missouri from 1997 to 2017 using a Burkard device operated according to National Allergy Bureau specifications. Data was stored in an Access database. The beginning of ragweed season was designated to be the date when the first 1% of the total yearly ragweed pollen grains was collected and the end of ragweed season was designated to be the date when 99% of the total yearly ragweed was collected.
The earliest day for the beginning of ragweed season was 8/2/2009 and the latest date for the end of the season was 11/10 2012. The year with the shortest ragweed season was 2005 with only 37 days of exposure. And, the year with the longest season was 2016 with 88 days of exposure. A plot of year and days in ragweed season has a correlation of 0.6 and a positive slope of 0.24.
We conclude that in response to warmer climactic conditions over the past 20 years ragweed season in the central Midwest US is starting earlier and ending later resulting in a longer duration of ragweed pollen exposure.