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We're not going to terraform Mars, but we're doing a good job of venusforming Earth.
(fediscience.org)
A "Showerthought" is a simple term used to describe the thoughts that pop into your head while you're doing everyday things like taking a shower, driving, or just daydreaming. A showerthought should offer a unique perspective on an ordinary part of life.
The good news is that it will never get to that point. Venus is a different planet with a different makeup and history.
The bad news, it doesn't have to get nearly that bad to be bad for us and the rest of existing life. Not even close. Just a few degrees more, and we're doing really well in getting there.
I’ve heard of the runaway greenhouse gas effect. Is there a limit to that?
The limit is our distance from the Sun. After a certain point the greenhouse gasses can't make up for the fact that we just get less radiation than Venus does. The maximum potential I've seen is 10°C - almost all life would go extinct and we'd have to live on the tropical Antarctic archipelago, but not Venus.