The only probable doomsday scenario of relevance I can think of is an asteroid impact.
While the danger from asteroid impacts is not negligible, media usually fail to report (or to stress) the calculated probability for an impending close encounter (one of the next is in 2036 Apophis, but the probability of a hit is about 1 in 40,000 - although figures vary from source to source, and that is exactly what sensational media reports have only in fine print, if at all).
The effects of any impact can be calculated here with my favorite impact calculator
http://www.lpl.arizona.edu/impacteffects/
P.S.: One funny doomsday headline I remember 1979 or 1980, when the German tabloid BILD headlined: "THE SUN IS EXPLODING!" together with a menacingly big picture of the sun (as far as I remember). It turned out they were just reporting on a heightened solar activity along with magnetic storms which is normal for a solar maximum every 11 years.