Temporal changes in the power of the long-wave radiation of the system “Earth — atmosphere” which is emitted to space always lag behind changes in the power of absorbed solar radiation due to slow change of its enthalpy. Long-term changes in the energy of solar radiation received by the Earth during a time interval determined by thermal inertia remain uncompensated by the energy emission to space. That is why the debit and credit parts of the average annual energy budget of the terrestrial globe with its air and water envelopes are practically always in an unbalanced state which is a basic state of climatic system. Average annual balance of the thermal budget of the system “Earth — atmosphere” during a long time period will reliably determine the course and value of an energy excess accumulated by the Earth or an energy deficit in the thermal budget and, with consideration for data of the TSI forecast, can define and predict well in advance the direction and amplitude of the forthcoming climate changes. From early 1990s, some decrease in the TSI has been observed. Since the Sun is now approaching the phase of bicentennial luminosity decrease, the Earth as a planet will henceforward have negative balance in the energy budget which will result in a temperature drop in approximately 2014. Due to an increase of albedo and decrease of the atmospheric concentration of green-house gases, the absorbed portion of solar energy and the influence of the green-house effect will additionally decline. The influence of the consecutive chain of feedback effects which can lead to an additional drop of temperature will surpass the influence of the TSI decrease. The onset of the deep bicentennial minimum of the TSI is expected in approximately 2042±11 and the on set of the 19th Little Ice Age during the past 7500 years is anticipated in 2055±11.