Here is a summary of what the geologic record tells us about abrupt climate change. This has nothing to do with global warming, but much of this information gets haphazardly and incorrectly tossed about in the global warming debate by both critics and proponents.

The existence of these rapid changes in not controversial
http://www.ncdc.noaa.gov/paleo/abrupt/index.html

Of course some of you will find this one controversial because of the ice core link to temperature and greenhouse gasses over the past several hundred thousand years.
http://www.ncdc.noaa.gov/paleo/globalwarming/index.html

You know you're in for a rough night at sea when the barometer does this: