Changes in phenology, the timing of seasonal events in plants and animals, are sensitive indicators of environmental change. Analysis of over 30 years of data from Europe shows that spring events, such as leaf unfolding, have advanced by 6 days, while autumn events, such as leaf colouring, have been delayed by 4.8 days. This results in an average lengthening of the growing season by 10.8 days since the early 1960s, primarily due to rising temperatures. The International Phenological Gardens (IPG) network, covering a wide range of latitudes and longitudes in Europe, has been used to study these changes. Phenological data from 1959 to 1993 show that spring phases are sensitive to temperature, with a potential advance of up to six days per 1°C increase in winter temperature. Linear trends in phenological data reveal that spring phases generally show a negative trend (earlier start), while autumn phases show a positive trend (later start), though some regional variations exist. Analysis of 616 spring data series shows a negative trend of -0.20 days per year, equivalent to a 6-day advance over 30 years. Autumn data series show a positive trend of +0.16 days per year, equivalent to a 4.8-day delay over 30 years. These results are supported by regional studies, including earlier flowering in Hungary and advances in spring and delays in autumn in Germany. The lengthening of the growing season is attributed to global warming, with temperature increases being a key factor. This change is likely to contribute to increased biomass formation, part of a global increase in biospheric activity. The results align with satellite data and CO₂ data, showing a global advance in the growing season. The study confirms that the observed changes are primarily due to temperature increases, with implications for future forest growth and ecosystem dynamics.Changes in phenology, the timing of seasonal events in plants and animals, are sensitive indicators of environmental change. Analysis of over 30 years of data from Europe shows that spring events, such as leaf unfolding, have advanced by 6 days, while autumn events, such as leaf colouring, have been delayed by 4.8 days. This results in an average lengthening of the growing season by 10.8 days since the early 1960s, primarily due to rising temperatures. The International Phenological Gardens (IPG) network, covering a wide range of latitudes and longitudes in Europe, has been used to study these changes. Phenological data from 1959 to 1993 show that spring phases are sensitive to temperature, with a potential advance of up to six days per 1°C increase in winter temperature. Linear trends in phenological data reveal that spring phases generally show a negative trend (earlier start), while autumn phases show a positive trend (later start), though some regional variations exist. Analysis of 616 spring data series shows a negative trend of -0.20 days per year, equivalent to a 6-day advance over 30 years. Autumn data series show a positive trend of +0.16 days per year, equivalent to a 4.8-day delay over 30 years. These results are supported by regional studies, including earlier flowering in Hungary and advances in spring and delays in autumn in Germany. The lengthening of the growing season is attributed to global warming, with temperature increases being a key factor. This change is likely to contribute to increased biomass formation, part of a global increase in biospheric activity. The results align with satellite data and CO₂ data, showing a global advance in the growing season. The study confirms that the observed changes are primarily due to temperature increases, with implications for future forest growth and ecosystem dynamics.