More days with higher temperatures throughout the decades have lead to increased levels of airborne pollen. The Asthma and Allergy Foundation of America found that the allergy season is growing each year as trees and plants are pollinating earlier and for a longer time. Besides warmer temperatures, high levels of carbon dioxide in the atmosphere also contribute to increasing the amount and potency of pollen a plant produces, according to a US Department of Agriculture study on ragweed. For more information, read the full article here.