Venus’s runaway greenhouse turned a wetter past into an oven
Climate models and atmospheric clues suggest early Venus may have held liquid water for a time before a runaway greenhouse boiled oceans away and baked CO₂ into a crushing air blanket.
As sunlight warmed the surface, more water vapor — a greenhouse gas — entered the air, trapping still more heat until the oceans could not survive. Solar brightening over geologic time made escape harder to reverse.
Venus is habitability’s cautionary twin. It shows a rocky planet near the Sun can lose surface water permanently and lock into a climate Earth carefully avoids.
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