Phenological Anomalies in St. Petersburg in the Third Decade of the 21st Century

In the third decade of the 21st century in St. Petersburg, phenological anomalies are most pronounced in the Spring Revival subseason; both of its phenomena begin at a significantly early date, with great anticipation. This has led to especially early blooming of gray alder as an indicator of the first stage of the Spring Revival subseason. The second most powerful anomaly occurs at the second stage of the Beginning of Summer subseason and lasts almost until the end of the calendar year, including Prewinter. At the same time, the summer phenomena are ahead of schedule, and from the Beginning of Autumn subseason, the phenodates abruptly reverse their sign. All phenological stages and subseasons of autumn began to occur at a late date. For the first time, in some years, the Beginning of Autumn subseason fell 12 days (2022) and 18 days (2024) later, and the second stage of the Beginning of Autumn subseason in 2024 began 16 days later than the norm of the climate in the 30-year period of 1980–2009. The duration of the Winter season decreased 9 days by 2021–2024, and the summer season increased 11 days. In the context of ongoing and increasing climate warming, the importance of phenological observations and the need for continuous monitoring are increasing. The role of botanical gardens as biodiversity conservation centers is increasing.