Understanding the causes of climate change at different time scales is still at the stage of framing scientific hypotheses, and hence requires further detailed investigation. Unfortunately, since climate change is by definition, a long-term phenomenon, it is very difficult to prove or disprove hypotheses. We have an abundance of hypotheses and a dearth of detailed long-term data. Nevertheless, where data exist, we should prefer data to computer models. Most cyclic and secular variations in sea ice conditions are rooted in atmospheric and oceanic processes that are influenced by both external and internal factors. The external factors include such helio- and geophysical impacts as solar activity, tidal and nutation phenomena, Earth's rotation speed, fluctuations in the solar constant due to changes in distance between the Earth and the Sun, fluxes of energy and charged particles from space, and other astronomical factors. Internal factors encompass natural hydrometeorological, geological, and biological processes and self-oscillation phenomena related to interactions in the lithosphere-ocean-sea ice-atmosphere-land system, with the latter including glaciers, rivers, etc. Anthropogenic factors or impacts that may augment internal system variables are associated with increased concentrations of greenhouse gases in the atmosphere and generation of black carbon soot and sulfate aerosols, due to human activities and their putative impact on climate.
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