The paper outlines the physical mechanisms of the greenhouse effect in the atmosphere. It describes the role of the greenhouse effect in controlling thermal parameters in the atmosphere, emission characteristics of CO2 and water vapor emission characteristics. Water vapor is shown to be the major determinant of the greenhouse effects in the atmosphere. The contribution of other gases, including CO2, is really minor. It is shown that absorption coefficients for the key greenhouse gases tend to decrease while temperature increase, which implies that the greenhouse effect becomes less intense at elevated temperatures in the atmosphere. Long-term climate research data are recalled, obtained on the basis of isotope tests of glacier layers and composition of sediments on the sea and ocean floor, indicating that the air temperature near the Earth surface has displayed large fluctuations when measured in the long-term, and the reasons for these fluctuations are not sufficiently well known. In the light of this research data, attributing all climate changes and anomalies to the CO2 emission only, seems to lack proper justification.