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Carbon Dioxide cause of Rising Pollen Levels and Hay Fever

Suffering from increasingly severe bouts of hay fever over a longer period of time? Scientists at this year’s European Geosciences Union (EGU) meeting might have the answer. Presentations at this annual event included a study conducted by researchers representing 13 European countries which argues that carbon dioxide emissions may be the cause of Europe’s rise in hay fever cases.

BBC environment correspondent, Richard Black, reports that the scientists have linked the increase in diagnosed hay fever cases to the rise in carbon dioxide emissions, which the scientists argue is the cause of higher pollen particles in the air. They arrived at this answer largely by elimination. The scientists had three hypotheses: that the increase in pollen levels in the air was due to higher temperatures, land use changes or the increase in carbon dioxide levels. But when comparing pollen levels during years with cooler temperatures to levels in years of warmer temperatures, scientists found an insignificant difference between the two. Land use changes are also not observed to be the associated with higher pollen levels, so the only cause the scientists could identify was the CO2 effect.

Experiments both in the real world and in special climate chambers support the hypothesis that increased CO2 levels do promote the production of pollen from certain trees. However, the study, based on data from pollen monitoring stations in 13 European countries, showed that not all tree species experienced an increase in pollen production levels. Out of the 25 species studied, only 60% of trees had increased pollen production, including nine species that are known to produce pollen that causes allergic reactions.

The study also showed that trends in pollen levels varied across countries, with some countries even showing a drop in pollen counts. Perhaps the most interesting find was that pollen tends to increase with CO2 levels in urban environments, but not outside cities. Researchers hypothesize that this could be due to ozone molecules. Outside the cities, these molecules tend to have a longer lifetime, and have been known to interfere with plant growth.

Europe has seen a dramatic increase in the allergic rhinitis in recent years. Between 2001 and 2005, cases of allergic rhinitis, including hay fever, have risen by 30%. The length of the pollen season has increased as well, with Germany reporting that only November is an allergenic pollen-free month.

To help alleviate the suffering, town planners and other tree planters should avoid species that produce allergenic pollen, including the popular birch tree.