Olive growing is very important economic potential in agricultural production of many countries in Mediterannean basin, including Croatia as well. Since the Mediterranean is the most endangered area in Europe regarding to climate changes, by using calculated active temperature sums, for five phenological stages of olive, we can monitor their changes in Dalmatia, in the periods 1981 – 2010 and 1986 –2015 so that we could compare them with reference period 1961 – 1990. The increase in temperature sums is more expressed in phenological stages which are appearing in autumn. In Dalmatia, the mean amount of percipitation and sunshine duration, from one phenological stage to another, is showing decreas in amount of percipitation and increase of sunshine hours from reference period to now. Reaserch results of this aktiv temperature sums were applied in a reconstruction of phenological stages in the past. Series of phenological data is prolonged for station Hvar in the period 1877 –2015 by phenological data from the period 1961 – 2015. Linear trend estimation of secular series of calculated olive phenophases showed statistically significant earlier onset of all flowering phenophases from -5 days to -6 days/100 years and earlier appearance of first ripe fruits by -21 days and harvest by -27 days/100 years. The big shift of earlier beginning autumn phenophases is indicating that climate changes are real and that they are gonna impact cultivation of olives in future. During dormancy, olive needs to accumulate enough inactive temperature sums with temperature treshold below 7 °C so that inflorescence buds could be determined. However, warmer and warmer winter are bringing many uncertainties which could effect immense consequences on olive growing if agricultural practices are not gonna be adapted on a new weather conditions.