The effects of climate change on the birch pollen season in Denmark

Abstract

During the last two decades the climate in Denmark has become warmer and in climate scenarios (IPCC, 2001) it is foreseen that the temperature will increase in the coming decades. This predicted future increase in temperature will probably affect both the flowering of plants and the dispersion of pollen in the air. In this study the already observed effects on the birch pollen season are studied. Trend analyses of the birch pollen season for two stations in Denmark more than 200 km apart give similar results. In Copenhagen there is a marked shift to an earlier season - it starts about 14 days earlier in year 2000 than in 1977, the peak-date is 17 days earlier and the season-end is 9 days earlier. For Viborg the trend to an earlier season is in general the same, but slightly smaller. During the same period there has also been a distinct rise in the annual-total amount of birch pollen, peak-values and days with concentrations above zero. Rising mean temperatures during winter and spring can explain the calculated trends toward earlier pollen season. Models for estimation of the starting date based on Growing Degree Hours (GDH's) give very fine results with a correlation coefficient around 0.90 and rms error around 4.2 days. For annual-total there is a significant positive correlation with the mean temperature in the growing season the previous year.