Records of different pollen were used to examine associations with weather parameters for the three different pollen: hazel (Corylus sp.), birch (Betula sp.) and grass (Poaceae). As air temperature is expected to rise according to the forecasts from the Intergovernmental Panel on Climatic Change (IPCC) and as this factor has a great potential to affect the development of plants, the records of different pollen were used to understand possible associations. The analysis of weather data for the studied period showed a significant increase in the annual mean temperature. From an aerobiology point of view it is most important to note that the temperature increase in winter (December) becomes most evident. As a consequence of this, hazel started earlier to flower. The flowering period which was originally in March thus shifted to January and February. Therefore the time period for hay fever patients shifted also partly to the traditional winter period. The starting season for birch and grass was not that much influenced by the temperature shift. However, regarding these two plants I also found that the warmer the weather preceding the flower period, the earlier the plants start to emit pollen. The total pollen count increased for the observed time period for all three investigated tare. The reason for this increase is not obvious, but it is conceivable that the observed temperature rise may exert an influence. The observed pollen count increase goes hand in hand with the observed increase in pollen allergies. However, a direct link could not be ascertained yet. The increase of temperature and the corresponding shift of the flowering time of plants whose pollen are of special interest in this connection has a medical significance since the period for hay fever sufferers becomes longer and can nowadays last from January (starting with hazel) until September (ending with mugwort) in Switzerland. In addition, the analysis of weather data showed that the amount of precipitation did not change significantly over the observed time period, although precipitation increased slightly. A strong negative correlation between pollen number and the amount of precipitation was especially found for birch and grass.
