claim: If there is  a cloud cover, the heat is trapped by water vapour as a greenhouse gas  and the temperature stays quite warm.
evidence: The large amount of CO2 in the atmosphere together with water vapour and sulfur dioxide create a strong greenhouse effect, trapping solar energy and raising the surface temperature to around 740 K ( 467 °C ), hotter than any other planet in the Solar System, even that of Mercury despite being located farther out from the Sun and receiving only 25% of the solar energy ( per unit area ) Mercury does.