Fans of Cormac McCarthy's novel The Road may have been disappointed when viewing the preview for the film as it attempts to explain the events that lead to America being devastated by an "unnamed cataclysm" The novel never explains what lead to the end of civilization and post-apocalyptic wasteland, however, the event is open to the reader's interpretation. 

If you’ve never read a page of The Road, you probably see the beginning of that trailer and think “End of the world action thriller. Cool.” If you indeed had that reaction, consider yourself officially misled.

Here’s a dose of the truth: The film version of The Road adheres pretty closely to the novel (with a few choice liberties taken here and there). In the novel, there is never any explanation of what event(s) turned America into a desolate wasteland. When the story begins, The Man (Viggo Mortensen) and The Boy (Kodi Smit-McPhee) are simply walking on the road across the annihilated landscape and that’s as much background as we get. There is no preachy message about the environment or nuclear war or human relations - no subversive political or religious metaphor. The story is set in a post-apocalyptic hell mainly because that setting is the most extreme contrast to the guarded and filtered reality in which most parents try and raise their kids.

Basically, "the studio producing the film...pulled out some dirty PR tricks to sell The Road to a wide audience".

Phew.

A review of the book can be found at Brown Noise Unit. Hans Fruck interprets it as a possible "post-nuclear-war America":

The sun's blotted out, the trees are bare and burnt, and everything’s swathed in ashes. This is the setting of Cormac McCarthy's The Road – post-nuclear-war America, or at least what used to be America. What's left is a charnel house. Barren earth, ash-choked rivers, corpse-littered landscape.

The story starts several years after the apocalypse. Already everything’s slumped into horrific, gut-churning violence. Those unlucky enough to survive creep, starving, through a hellish landscape, hiding from the cannibals that stalk the countryside, and battling just to see the next day, and the next. Amid this panoply of horrors, the smallest act of endurance is the rawest act of bravery....

I'm with Hans and not with the "Climate Change" marketing schtick.