In other frightening news -- Large Solar Activity could cost 2 trillion

[racemize]

http://science.nasa.gov/science-news/science-at-nasa/2009/21jan_severespaceweather/

 

Normally wouldn't pay too much attention, but it is from nasa.  Given that there was a small one in 1989, a 10x one in 1921, and an even bigger one in 1851, it doesn't seem too far out of the question that a relatively large one could happen in the next 50 years.

 

Really big ones are apparently more rare (from http://en.wikipedia.org/wiki/Solar_storm_of_1859):

Ice cores contain thin nitrate-rich layers that can be used to reconstruct a history of past events before reliable observations. These show evidence that events of this magnitude—as measured by high-energy proton radiation, not geomagnetic effect—occur approximately once per 500 years, with events at least one-fifth as large occurring several times per century.[9] Less severe storms have occurred in 1921 and 1960, when widespread radio disruption was reported.

 

Other links:

http://www.nap.edu/openbook.php?record_id=12507&page=1

 

Probably not too useful for investing if the worst case happens, though.