It has almost come to the point where the time when the first pollen of the new pollen season appears overlaps with the time when the last pollen of the previous pollen season disappears. On the one hand, climate change causes the pollen of grasses and herbs to persist longer into autumn, while on the other hand, trees begin to flower earlier in the year. Most affected are people allergic to hazel and alder pollen. Hazels and alders are extremely sensitive to temperature and begin to flower during prolonged mild phases during the winter months. In the wake of climate change, these mild phases are occurring more frequently in Germany and the temperatures reached are also higher than in the past, as the record high temperatures at the turn of the year 2022/2023 clearly showed. Where in the past, temperatures barely reached 10 °C under similar weather conditions, today they can quickly reach 15 °C and more. The pollen of the early-flowering tree species is released correspondingly quickly and early in the year.
The 2023 pollen season in the southwest of Germany began on the very first day of the year with record-breaking pollen concentrations and in some places already high hazel pollen counts – a first in measurement history. This trend towards early pollen exposure is reinforced by the new planting of allergenic tree species in cities, including, for example, the non-native and climatically hardy purple alder, which tends to release its pollen as early as around Christmas time, weeks before the native alders.
The European Centre for Allergy Research Foundation – ECARF and the PID Foundation therefore recommends allergy-friendly planting in cities, avoiding trees that release allergenic pollen.