Doclady Earth Science, 425 (2), pp. 419-423, 2009 This work is dedicated to study of the nature of decadal variations observed in climatic data. As a result of the wavelet analysis of instrumental time series of global temperature and phase relations in the variations of the solar and volcanic activity in the period 1880–1995, it was shown that the combined inﬂuence of solar and volcanic activity on the climate is the cause of decadal variations in the global temperature observed in the second half of the 20th century. The phase relations between strong volcanic eruptions and solar cycles played the key role in this process. The solar signal manifests itself in the climate variations only if the corresponding phase correlation of the volcanic activity to the solar cycle is considered. In this case, favorable conditions are formed for intensiﬁcation of decadal climatic ﬂuctuations as occurred in the second half of the 20th century after strong volcano eruptions.