[Effect of climatic changes on the phenology of plants and the presence of pollen in the air in Switzerland]

The phenologic observations carried out in Switzerland since 1951 show a clear tendency to the earlier appearance of the spring phases of development of the vegetation during last decades. As these phases are strongly influenced by the temperature, these results reinforce the hypothesis according to which the climatic reheating in progress strongly influences the development of the vegetation. The flowering and the release of the pollen of the plants allergens are significant phenologic phases for human health. Modifications in their dates of manifestation lead to a displacement of the periods of allergic risk. The analysis of the aerobiologic data of the Swiss stations over one duration of more than 20 years showed that the species which flower in winter and in spring were subject to the influence of the soft winters of the years 1990 to 2000. In certain areas the pollen of birch, for example, is nowadays waited on average 3 weeks earlier than 20 years ago, whereas the pollen of ash appears with one month in advance. The phenologic and aeropalynologic studies thus prove sensitive witnesses of the climatic change in progress. This last intervenes like an indirect but significant component of human health, in particular when the field of the allergies is considered.