The impacts of climate change and meteorological factors on pollen season indicators of allergenic plant taxa

Pollen respiratory allergies have been increasing in prevalence over the last two decades, partly as the result of the impact of climate change. For many allergenic trees, grass and weed species, increased pollen production and prolonged pollination period result in long-term increased abundance of pollen allergens in the atmosphere; earlier shifts of airborne pollen grains and prolonged exposure to respiratory allergens with important health effects on allergic individuals. The aim of this review paper was to investigate the impact of climate change and meteorological factors on pollen season indicators with a special focus on the main allergenic taxa worldwide. Main variables influencing flowering phenology such as location, climatic and meteorological parameters were identified, discussed and substantiated by published literature. Temperature, solar radiation, humidity, rainfall, wind speed and direction were identified among the most important meteorological parameters affecting the fluctuations of annual concentrations of allergenic airborne pollen grains. Although notable variations were observed according to allergenic species and studied geographical areas, temperature appeared to be the most important climatic parameter affecting flowering phenology and pollen season indicators, especially in tree species. Rising carbon dioxide levels also result in increased plant biomass, increased flowering intensity and pollen production in several tree, grass and weed allergenic species. In the light of this review, there is a growing body of evidence supporting the effect of climate change on the flowering phenology and pollen season indicators of a substantial number of allergenic ornamental and invasive plant species.