Pollen Season Trends (1973-2013) In Stockholm Area, Sweden, — 40 Years Of Climate Change And The Possible Health Effects

Abstract

Introduction: The increase in global average temperatures affects the phenological patterns of plants, including the timing and length of the pollen season. Changes in the temporal distribution of airborne pollen are likely to affect the exacerbations of allergic airway diseases and the associated public health burden. In the Stockholm region of Sweden, continuous monitoring of airborne pollen has been performed since 1973. Methods: In the present study, the temporal and quantitative changes in the pollen seasons between 1973 and 2013 were studied for nine types of pollen. Linear regression models were used to estimate the long term trends in duration, start- and end-dates, peak-values and the yearly accumulated pollen sums of the pollen seasons. Results: The pollen seasons of several species (e.g. birch, oak and pine) were found to start significantly earlier today compared to 40 years earlier (14 days earlier in birch), and have an earlier peak-date (16 days earlier in birch and oak), while the season of other species seemed largely unaffected. However, the long term trends in the end-dates of pollen seasons differed between early and late flowering species. For late-summer/early-autumn flowering species (grass and mugwort), a significant change towards later end-dates (14 days later in mugwort) was observed and the duration of season was found to have increased. A significant trend towards an earlier end-date was also found in the majority of the spring/early-summer flowering species (i.e. elm, oak, pine and birch), but the length of the season seemed unaffected. Conclusions: Given the earlier start-dates of the early flowering species and later end-dates of the late flowering species, the total period of pollen exposure has increased since 1973 with up to 30 days, this change is liekly to affect the temporal pattern of the health effects in pollen-sensitized persons.