People, and particularly intellectuals, tend to over-react to environmental and other social problems, making use of incorrect data or fallacious arguments (whether deliberately or inadvertently) to promote environmental scares.
Intellectuals use each other to verify the state of the world. They depend most upon the experience of members of their own social network, but may also find incidents credible if they are observed by friends of friends. The sense of subjective probability is even influenced by reports of experiences twice removed. Reality testing works quite well as long as the networks remain constant in size, but social networks are doubled or trebled when people are in their twenties and thirties and are then usually maintained intact until the aging process makes itself felt, without the people themselves being conscious of the expansion. Therefore the threatening events coming to their attention per month increase by a factor somewhere around three to ten, depending upon the degree of overlap in social networks. The impression is reinforced and magnified further when they hear that such an impression is the virtually unanimous experience of everyone they meet in their circle. If one adds to this the improvement in communications which ensures that news travels faster and is less likely to be lost in a terminated rumour chain, it becomes evident that it would be a statistical miracle to find an optimist.
All doomsday scenarios, religious or otherwise, seem to fulfill people's self-righteous tendencies: like sexual diseases, doomsday is seen as punishment for something wicked one has done. They relieve the burden of free will, providing an assured destiny and a certain future.