The length of the ragweed season has been extended by 2-weeks in some
northern US states and by about a month in some areas of Canada, according to Agricultural
Research Service at the U.S. Department of Agriculture, in Beltsville, Md. Ragweed
allergies are very common in the US with at least 1 in 10 people sensitive to
ragweed pollen. At least 10% of the US population is sensitive to ragweed in summer
and fall, which along with pollen can cause hay fever and asthma. Over the past
three decades the prevalence of this allergic disease has been increasing in the
Experts attribute this increase to changes in the global climate which is increasing the duration of exposure to allergens. However they haven't been able to explain the exact reason behind this.
To test the hypothesis, scientists studied the pollen data from the past 15years from eight different locations in US and two locations in Canada. They found that in seven locations, north of 40 degrees latitude, the number of days in the ragweed pollen season had increased between 1995 and 2009. Study author and plant physiologist Lewis Ziska said, "This study is a confirmation of what the Intergovernmental Panel on Climate Change has been projecting.
Ziska said, "If this trend continues, and we see greater warming to the poles, allergy seasons will be different and, for some, they'll be extended."
Chief of the section of Allergy, Asthma and Immunology at Children's Mercy Hospitals and Clinics in Kansas City, Dr. Jay Portnoy said, "For people who have experienced mild ragweed seasons, they may experience more problems than in the past.
This may change the timing of preventive medications, and for physicians trying to diagnose allergic disease, they may need to change their assumptions about what's in the air."