Evidence of Solar Variation in Tree-Ring-Based Climate Reconstructions

Analyses of the summer temperature anomalies in northern Fennoscandia for A.D. –1991 and mean annual temperature in the northern hemisphere for A.D. 1000–1990 (both reconstructed by means of dendrochronological methods) are performed using Fourier and wavelet approaches. It is revealed that the century-type (65–140 yr) periodicity is present in both series during most of the full time range. A comparison of the northern Fennoscandian temperature record with a variety of indicators of solar activity (direct measurements and proxies) shows that this century-scale periodicity most probably was forced by a centennial cycle of solar activity (Gleissberg cycle). Despite the fact that the connection between the centennial variation of global northern hemispheric temperature and that of the Sun's activity is weaker, a link between the two can also not be excluded. The results obtained give us new evidence of the reality of the solar–climate link over a record long-time scale (at least during the last millennium). Variable length of the century-long temperature periodicity may reflect the corresponding changes in the length of the Gleissberg solar cycle. The effects, which can obscure the Sun's influence on the global hemispheric climate, are discussed.