<sod>  
 He was well known as a coauthor of the paper that warned of the dangers of [[nuclear winter]]. He also perceived [[global warming]] as a growing, man-made danger and likened it to the natural development of [[Venus (planet)|Venus]] into a hot life-hostile planet through [[greenhouse gas]]es.  His interest in these topics was in large part motivated by his interpretation of the [[Drake equation]] and the [[Fermi paradox]].  He believed that the Drake Equation suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations suggests that technological civilizations tend to destroy themselves rather quickly. This stimulated his interest in identifying ways that humanity could destroy itself, with the hope of avoiding such destruction and eventually becoming a space-faring species.
 
He wrote (with [[Ann Druyan]], whom he later married) and narrated the highly popular thirteen part [[PBS]] television series ''[[Cosmos: A Personal Voyage|Cosmos]]''; he also wrote books to popularize science (''The Dragons of Eden'' (which won a [[Pulitzer Prize]]), ''Broca's Brain'', etc.) and a novel, ''[[Contact (novel)|Contact]]'', that was a best-seller and had a [[Contact (movie)|film adaptation]] starring [[Jodie Foster]] in [[1997]]. The film won the [[1998]] [[Hugo award]].  From ''Cosmos'' Sagan became associated with the catchphrase "billions and billions" which he never actually used in the television series.  (He simply often used the word "billions.")  Late in his life, Sagan's books developed his skeptical/atheist view of the world, including ''The Demon-Haunted World: Science as a Candle in the Dark'' and ''Billions and Billions: Thoughts on Life and Death at the End of the Millennium'', which includes Ann Druyan's account of Sagan's death as a non-believer.
 
 Sagan caused mixed reactions among other professional scientists.  On the one hand, there was general support for his popularization of science, his efforts to increase scientific understanding among the general public, and his positions in favor of [[skepticism]] and against [[pseudoscience]].  On the other hand, there was some unease that the public would misunderstand some of the personal positions and interests that Sagan took as being part of the scientific consensus rather than his own personal views, and there was some unease, which some believe to have been motivated in part by professional jealousy, that scientific views contrary to those that Sagan took (such as on the severity of nuclear winter) were not being sufficiently presented to the public.
 
 <eod> <sod> 
 He was well known as a coauthor of the paper that warned of the dangers of [[nuclear winter]]. He also perceived [[global warming]] as a growing, man-made danger and likened it to the natural development of [[Venus (planet)|Venus]] into a hot life-hostile planet through [[greenhouse gas]]es.  His interest in these topics was in large part motivated by his interpretation of the [[Drake equation]] and the [[Fermi paradox]].  He believed that the Drake Equation suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations suggests that technological civilizations tend to destroy themselves rather quickly. This stimulated his interest in identifying ways that humanity could destroy itself, with the hope of avoiding such destruction and eventually becoming a space-faring species.
 
He wrote (with [[Ann Druyan]], whom he later married) and narrated the highly popular thirteen part [[PBS]] television series ''[[Cosmos: A Personal Voyage|Cosmos]]''; he also wrote books to popularize science (''The Dragons of Eden'' (which won a [[Pulitzer Prize]]), ''Broca's Brain'', etc.) and a novel, ''[[Contact (novel)|Contact]]'', that was a best-seller and had a [[Contact (movie)|film adaptation]] starring [[Jodie Foster]] in [[1997]]. The film won the [[1998]] [[Hugo award]].  From ''Cosmos'' Sagan became associated with the catchphrase "billions and billions" which he never actually used in the television series.  (He simply often used the word "billions.")  Late in his life, Sagan's books developed his skeptical/atheist view of the world, including ''The Demon-Haunted World: Science as a Candle in the Dark'' and ''Billions and Billions: Thoughts on Life and Death at the End of the Millennium'', which includes Ann Druyan's account of Sagan's death as a non-believer. 
He also wrote '''Pale Blue Dot: A Vision of the Human Future in Space''', 
which was selected as a notable book of 1995 by The New York Times.

He cofounded the '''Planetary Society''', a society created to 
do major research in radio communication with extraterrestrial life, 
robotic exploration on [[Mars]], the investigation of asteroids near the 
[[Earth]].
 
 Sagan caused mixed reactions among other professional scientists.  On the one hand, there was general support for his popularization of science, his efforts to increase scientific understanding among the general public, and his positions in favor of [[skepticism]] and against [[pseudoscience]].  On the other hand, there was some unease that the public would misunderstand some of the personal positions and interests that Sagan took as being part of the scientific consensus rather than his own personal views, and there was some unease, which some believe to have been motivated in part by professional jealousy, that scientific views contrary to those that Sagan took (such as on the severity of nuclear winter) were not being sufficiently presented to the public.
 
 <eod>