"The chances of global disaster" by John Silveira
Some possible disruptions to life as usual are presented with some reasons given for their likelihood of happening. Likely disruptions are nuclear war, pandemic, volcanism, an ice age, and comet and asteroid impacts.
The several largest past volanic eruptions are briefly described. The explosion of a comet over Siberia about a century ago is briely described. Estimates of the probabilities of future impacts by comets and asteriods are given. The effects of impacts of particularly sized asteriods are detailed with comments about how each size might effect civilization.
The article seems to be mostly logical and informative but is presented as a possibly fictional narrative rather than factual and scientific. Some of the probabilities of particular calamities are more reasonable guesses than scientifically determined values.
Alan Detwiler, self sufficiency advocate and author, bio at http://www.smashwords.com/profile/view/alandetwiler