Want to see something that will scare the crap out of you?
This app at NOAA lets you graph temperatures for various years.
Graph for 1930-1934
http://www7.ncdc.noaa.gov/CDO/cdodiv...reqtype=nation
Graph for 2006-2010
http://www7.ncdc.noaa.gov/CDO/cdodiv...reqtype=nation
Open them up in two tabs of your browser and then tab back and forth.
OOOOOOOOOH. Scary.