The onset of seasons, as observed in the seasonal cycle in nature, has undergone major shifts during recent decades. Spring phenological phases, such as leaf unfolding and flowering, are continuously advancing.The onset of summer phases, such as flowering or fruit ripening, is also advancing. In contrast, the picture of autumn is more heterogeneous with partly later onset of leaf colouring and leaf fall.A new comprehensive European study (COST725) revealed that flowering and leaf unfolding in spring (75 218 records) have advanced by 2.5 days / decade over the last 30 years. In total the vegetation period in Central Europe is now up to two weeks longer than 30 years ago. This signal, which is most apparent in Germany and Switzerland in the mid 1980s, can be attributed to warming due to the anthropogenic greenhouse effect. This far-reaching study within the COST725 action further revealed that the advance of bud burst and flowering is not an accidental result of selected observational records, but is evident throughout Europe. Countries with larger warming have experienced stronger changes in nature.