OUT-OF-CONTROL GREENHOUSE EFFECT

Evaporated water may have triggered the greenhouse effect, which heated Venus to a temperature of 465 °C.

1 In its youth, Venus was probably

habitable with oceans on the surface and a tropical climate. This period lasted for the first two billion years of Venus’ life. 2 Venus is closer to the Sun than Earth is, and so, the liquid water on its surface evaporated faster. Water vapour is an efficient greenhouse gas that keeps out the cold. 3 Water vapour disappeared. Sunlight broke apart the water molecules. The oxygen bound to carbon, turning into CO , as 2 the hydrogen disappeared.

4 Now, the atmosphere consists of

96.5 % CO . The gas keeps in the heat 2 that – in spite of a thick cloud cover reflecting much of the sunlight – gets to the surface.