The examples of catastrophizing provided elsewhere tend towards the personal; they instruct one in the art of, say, drawing an imaginary line between the loss of one’s keys and the failure of one’s marriage. 
It should come as no surprise, though, that the same technique that can conjure catastrophic consequences from personal oversights can also be applied to the realm of the public, the global. 

Indeed, the environmental movement has largely depended on catastrophisms to make its case to the public: if we exterminate a sufficient number of tiny organisms, we imperil the world, etc... Environmentalists have the unenviable task of convincing people that something tiny, something seemingly totally irrelevant, can have an effect on every other living thing. 

While catastrophizing embraces no one creed or cause, the budding catastrophizer should in terms of process emulate the environmentalist: he or she should make a habit of selecting from the news what seems to be an innocuous fact and extrapolating from it a series of decidedly unfortunate events. The topic of environmental collapse, though, should be avoided if the catastrophizer is devoted to truly honing his or her craft as it is such a familiar source of catastrophizing. 

If you are concerned that your catastrophizing studies are impractical, if your hectoring parents are demanding to know how catastrophizing in your room for hours will lead to gainful employment, never fear. Or rather, don’t stop fearing. A study of history reveals that catastrophizers always have the last, mirthless, laugh.

Do you know what started the First World War? I do, because I checked Wikipedia:

The assassination on 28 June 1914 of Archduke Franz Ferdinand of Austria, the heir to the throne of Austria-Hungary, is seen as the immediate trigger of the war, though long-term causes, such as imperialistic foreign policy, played a major role. Ferdinand's assassination at the hands of Serbian nationalist Gavrilo Princip resulted in demands against the Kingdom of Serbia.[6] Several alliances that had been formed over the past decades were invoked, so within weeks the major powers were at war; with all having colonies, the conflict soon spread around the world.

One man is assassinated and ultimately the world is plunged into a war unlike any that had ever been seen before. How many men or women could have predicted that one shot would lead to such widespread devastation? Only the proto-catastrophizers (I, of course, am the original, founding catastrophzier).

It’s important, though, not to focus on events that are clearly worrisome, however small. The real challenge is to concentrate on a detail that appears to be totally inconsequential and to use that as the springboard for your catastrophism. Consider, if you will, the following sample catastrophism:

On November 10, 1955, a boy was born in Stuttgart, Germany; 
He was drawn to the world of film, and began creating his own stories in that medium; 
He directed a dangerously subversive film starring only non-actors (Independence Day); 
After most likely being unable to sign Nicholas Cage because of a scheduling conflict, he convinces John Cusack to sign on to a new project; 
Promotion for the film 2012 is ubiquitous and unremitting; 
A young girl in Toronto, having watched Say Anything numerous times during an impressionable period, becomes obsessed with 2012; 
She destroys the world.

I became bored by this catastrophism, or else it would have seemed more  complex and fluid. My point, however, should be clear: the birth of one future Hollywood film director can, in a totally unheralded fashion, herald the end of the world. Now, once a day select one apparently insignificant detail from the news and connect it to eventual global destruction. Catastrophizer’s orders.

POLITE DISCLAIMER: This site is intended for entertainment purposes only. If you are not entertained, fair enough.