Due to global warming, tree, grasses and weeds and ragweed produce more pollen over more weeks when temperatures and carbon dioxide levels rise.
Percentage of U.S. population who reported suffering from allergic rhinitis:
4.9% in 2000
6.4% in 2005
7.6% in 2000
8.2% in 2005
6.3% in 2000
7.4% in 2005
Source: Angency for Healthcare Research and Quality
Pollen-producing plants (weeds and trees) in Omaha, Nebraska
Big culprit for allergies? Evidence points to global change. USA Today.