The northernmost conifers in the world are located well above the Arctic Circle in the Taymir region of northern Siberia and have been recording the thermal environment for centuries to millennia. The trees respond to temperatures beyond the narrow season of actual cambial cell division by means of root growth, photosynthesis, lignification of cell walls, and other biochemical processes. Data from annual tree-ring widths are used to reconstruct May–September mean temperatures for the past four centuries. These warm-season temperatures correlate with annual temperatures and indicate unusual warming in the 20th century. However, there is a loss of thermal response in ring widths since about 1970. Previously the warmer temperatures induced wider rings. Most major warming and cooling trends are in agreement with other high-latitude temperature reconstructions based on tree-ring analyses with some regional differences in timing of cooling in the late 18th century and of warming in the late 19th century.

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The periodicity of climatic processes along the Russian Arctic Ocean coast has been studied by analyzing the tree-ring chronologies for the regions close to the northern timberline. The wavelet analysis of annual series of conifer tree rings for the period 1458-1975 has revealed climatic oscillations with periods of 20-25 years. The amplitudes and periods of climatic oscillations in the region of Russian Arctic Ocean proved to exhibit appreciable changes. Especially strong climatic variations in comparison with the recent ones were found to occur during the Maunder minimum epoch when the period of oscillations increased from 22-23 years to 24-29 years, and oscillations with periods of 15 years appeared. After the Maunder minimum, the periods of oscillations and their amplitudes again decreased, and the 15-16-year maximum disappeared. Analysis of solar activity based on of radiocarbon ( 14 C) concentration in annual tree rings has revealed a similar pattern in changes of periodicity before, during, and after the Maunder minimum. This suggests that quasibidecadal climatic oscillations and variations in solar activity can be connected with each other. A possible solar forcing of periodic climatic processes and its nonlinear influence on the atmosphereocean-continental system are discussed. The intense quasi-bidecadal climatic oscillations can be, in all probability, interpreted as resulting from amplification of a weak solar signal in the atmosphere-ocean system that has its own noises whose frequencies are close to the 22-23-year solar cycles.

Ogurtsov, M.G., Raspopov, O.M., Helama, S. Oinonen, M., Lindholm, M., Jungner, H. and Meriläinen, J., 2008: Climatic variability along a north-south transect of Finland over the last 500 years: signature of solar influence or internal climate oscillations? Geogr. Ann., 90 A (2): 141-150.ABSTRACT. Statistical analysis of a multi-centennial dendrochronological proxy dataset of regional climate, constructed across the latitudinal gradient of 1000 km, was performed. It was shown that centennial (c. 100 year), tri-decadal (27-32 year), bi-decadal (17-23 year) and decadal (9-13 year) periodicities governed the climate variability in Finland over the last five centuries. Despite the fact that many of the climatic periodicities bore great resemblance to periodicities of solar cycles, little evidence of actual solar influence on Finnish climate was found when the climate proxy records were subjected to linear correlation analysis with sunspot numbers. Highly non-linear response of Northern Fennoscandian climate to solar forcing might be a cause of this result, as well as influence of terrestrial climatic processes (e.g. effect of other forcing factors and internal dynamics of regional climate). Our results show that the presence of internal climate variability at time-scales of solar activity might distort the solar signature in climatic data and complicate its detection.