From VOA Learning English, this is the Health & Lifestyle report.
When Dr. Stanley Fineman started as an allergist, he told patients to start taking medications and prepare for pollen season in the middle of March.
That was about 40 years ago. Today, he tells them to start around the middle of February.
Since 1990, pollen season across the United States and Canada has been starting earlier, about 20 days earlier. And pollen loads, the amount of pollen released by plants, are 21 percent higher.
The main reason for this, a new study found, is global warming.
Other studies have shown North America’s allergy season getting longer and worse. But this one, published in the Proceedings of the National Academies of Sciences, has the most complete information coming from 60 reporting stations. It is also the first study to make scientific connections between an earlier and more intense pollen season with human-caused climate change.
The study says the warmer the Earth gets, the earlier spring starts for animals and plants, especially plants that release pollen. Additionally, trees and plants produce more pollen when they get carbon dioxide.