Climate change contributes to earlier, longer, and worse allergy seasons for millions in the U.S. that suffer from season allergies -- including 19% of children. HUNTSVILLE, Ala. — The first leaves and blooms of spring are arriving days to weeks early in the large parts of the southern and central U.S., according to the USA National Phenology Network. That's bad news for people with seasonal allergies -- about one-quarter of adults and one-in-five children in the U.S. Earlier springs, longer pollen seasons, and worse seasonal allergies are all linked to our warming climate