Climate change in Switzerland: Impact on hazel, birch, and grass pollen on the basis of half a century of pollen records (1969 - 2018).

As indicated by the Intergovernmental Panel on Climate Change (IPCC), human activities are estimated to have caused ~ 1.0 °C of global warming above pre-industrial levels. The impact of this global warming is diverse and pertains also plant biology. The start of the pollen season as well as the observed quantities of pollen have been considered indicators of the impact of climate change. Switzerland has one of the longest pollen time series now - more than half a century. It has been tested whether the impact of climate change is robust by checking with this long time series of different pollen like hazel, birch, and grass as prominent representatives of triggers of hay fever. The results indicate that based on a time series of 50 years, the pollen seasons of hazel, birch, and grass started earlier as the temperature increased. Comparing the annual amount of pollen, a relevant increase is only observed for hazel. However, it must be considered that in the observed 50 years there was a land use change from grass land to built-up land due to the increase of population, and yet certain pollen counts increased considerably.