I came across an article at Ars Technica on the implications of the recent wave of newly discovered exoplanets that fall within the Goldilocks zone. The author proposes that the discovery of planets that are viable for civilization but uninhabited could be the result of a pattern of bottlenecks for intelligent life referred to as the Great Filter:
This apparent absence of thriving extraterrestrial civilizations suggests that at least one of the steps from humble planet to interstellar civilization is exceedingly unlikely. The absence could be because intelligent life is extremely rare, or because intelligent life has a tendency to go extinct. This bottleneck for the emergence of alien civilizations from any one of those billions of planets is referred to as the Great Filter.
In the discussion of the latter possibility the author links to this BBC item on research into extinction-level threats to humanity. Surprisingly from the Beeb, anthropogenic global warming is not listed as one of those threats.