A warming climate is extending allergy seasons across the United States by increasing the number of days with temperatures above freezing, allowing plants to grow and release pollen for longer periods. This trend, coupled with rising carbon dioxide levels, exacerbates allergy-related health issues. Analysis by Climate Central, using NOAA data, reveals significant increases in growing season length from the 1970-1979 decade to the 2015-2024 period. For instance, the Northern Rockies & Plains saw a 69.6% increase in growing season length, from 112 days to 190 days. Overall, growing seasons have lengthened by over a month in some areas compared to fifty years ago, leading to more intense and prolonged allergy seasons for millions.