Any number of things...
Yellowstone erupting...
Half the main island of HI sliding off the shelf, wiping out Ohua and causing a tsunami that rips apart most of Asia...
And then there is that killer asteroid the Russians are supposedly freaking out about, building the world's largest bunker/continuity of government site whilst trying to figure out a way to save the world without the Americans help...
I love conspiracy theories for their their creativity.
One of my favorites has always been the one about what happened to over 100 Nazi u-boats. There are news reports of ships off of Argentina and Brazil being attacked by German pirates in u-boats.