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.

It is generally believed that the low-frequency variability of climatic parameters seems to be connected to solar cycles. The principal periodicities are: 11-year (Schwabe), 22-year (Hale), 33-year (Bruckner) and 80–100-year (Gleissberg) cycles. The main heliophysical factors acting on climate, the biosphere and the atmosphere are solar irradiance, the intensity of solar and galactic cosmic rays (relativistic charged particles with energies >500 MeV) changing the cloud cover of the atmosphere, and UV-B-radiation. The 11-year and 80–90-year solar cycles are apparent in solar radiation and galactic cosmic ray trends. At the same time the bidecadal Hale cycle, related to a reversal of the main solar magnetic field direction is practically absent in either solar radiation or galactic cosmic ray variations. Besides, nobody can identify any physical mechanisms by which a reversal in the solar magnetic field direction could influence climate. However, the 22-year cycle has been identified in rather many regional climatic (droughts, rainfall, tree growth near 68° N, 30° E) and temperature records all over the world. We discuss here three possible cause of the bidecadal periodicity in climatic records, one of which is associated with a variation of stardust flux inside the Solar System. The most recent observations by the DUST experiment on board the Ulysses spacecraft have shown that the solar magnetic field lost its protective power during the last change of its polarity (the most recent solar maximum), so that the stardust level inside of the Solar System has been enhanced by a factor of three. It is possible that the periodic increases of stardust in the Solar System may influence the amount of extraterrestrial material that falls to the Earth and consequently act on the Earth's atmosphere and climate through alteration of atmospheric transparency and albedo. This material (interstellar dust and/or cometary matter) may also provide nucleation sites and thereby influence precipitation.