Layers of Venus's atmosphere. Graph illustrating the variation of temperature and pressure against height in the Venusian atmosphere. The atmosphere is 97 percent carbon dioxide (CO2), the end result of a runaway greenhouse effect. The CO2 gas traps the heat of the Sun, raising the heat, baking CO2 from the rocks and raising the heat further. The surface temperature is over 750 Kelvins (477 degrees Celsius) and the atmospheric pressure at the surface is 90 times that of Earth. Earth-like temperatures and pressures occur at a 50-kilometre altitude where a layer of corrosive sulphuric acid (H2SO4) clouds covers the planet. Their reflection of sunlight accounts for Venus's brightness.