Allergy season is getting worse on a warming planet, experts say. Spring allergies start earlier; fall allergies last longer. With climate change causing allergen culprits including trees, grasses and weeds to release pollen for longer than in the past, experts say more research is needed to better predict pollen counts and prepare vulnerable populations — which include the 25% of adults in the country who have seasonal allergies, according to the Centers for Disease Control and Prevention. diseases. (JENNY WHIDDEN).