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gjm comments on Open Thread, Aug. 1 - Aug 7. 2016 - Less Wrong Discussion
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Well, we could look at other planets that show any sign of ever having had an Earthlike atmosphere. Here's (I think) the list of such planets we know about and are able to observe: {Venus}.
That might be a pretty bad sign, but I'm not sure Venus's history is similar enough to earth's. (E.g., whatever got its atmosphere the way it is, it probably wasn't overproduction of CO2 by burning fossil fuels. Though, actually, I'm not sure how we'd know.)
Venus doesn't have magnetic field. Because of it, Venus lost hydrogen from its atmosphere due to solar wind. Because of it Venus became very dry. So, it had not life and ways to fix CO2 in carbonates in water. It resulted in large accumulation of CO2 in atmosphere and strong greenhouse effect. It changed the way its mantle creates continents as dry mantle is not plastic. There is no plate tectonics on Venus. The surface changes every half a billion years in one large "supervolcanic" event.
There is also the little issue of Venus receiving about twice the insolation than Earth....
But Venus albedo is 0.75, while Earth's is 0.3. So Venus gets less solar energy than Earth, because of very white upper cloud cover http://www.universetoday.com/36833/albedo-of-venus/