Here is Carl Sagan's original essay on climate change in 1980 where he warned specifically about global cooling based on deforestation: https://gizmodo.com/heres-carl-sagans-original-essay-on-the-...
5 years later he testified to Congress about the dangers of excess CO2 emissions causing runaway warming: https://www.youtube.com/watch?v=Wp-WiNXH6hI
On the surface these two messages may seem contradictory but underlying both is a consistent message that excessive man-made changes to a delicate highly non-linear system are dangerous to our survival as a species.