It has been discovered that there appears to exist a close relationship between relative differences in total solar irradiance and the atmospheric temperature, at a pressure of 1 bar, on all three terrestrial-type bodies which possess thick atmospheres. The apparent relationship is through the quaternary root of total solar irradiance at 1 bar, and applies to the planetary bodies Venus, Earth and Titan. The relationship is so close that the average surface atmospheric temperature of Earth can be easily calculated to within 1 Kelvin (0.5%) of the correct figure by the knowledge of only two numbers, neither of which are related to the Earth's atmosphere. These are; the atmospheric temperature in the Venusian atmosphere at 1 bar, and the top-of-atmosphere solar insolation of the two planets. A similar relationship in atmospheric temperatures is found to exist, through insolation differences alone, between the atmospheric temperatures at 1 bar of the planetary bodies Titan and Earth, and Venus and Titan. This relationship exists despite the widely varying atmospheric greenhouse gas content, and the widely varying albedos of the three planetary bodies. This result is consistent with previous research with regards to atmospheric temperatures and their relationship to the molar mass version of the ideal gas law, in that this work also points to a climate sensitivity to CO 2-or to any other 'greenhouse' gas-which is close to or at zero. It is more confirmation that the main determinants of atmospheric temperatures in the regions of terrestrial planetary atmospheres which are >0.1 bar, is overwhelmingly the result of two factors; solar insolation and atmospheric pressure. There appears to be no measurable, or what may be better termed 'anomalous' warming input from a class of gases which have up until the present, been incorrectly labelled as 'greenhouse' gases.