[Tanada]

Here is an interesting study, this map shows an overlay of the changes between the 1961-1970 map and the 2001-2010 map, a full 40 years of changing zones. The black outlines are the airports where top quality instruments were available but most towns have weather stations that report to the government and this shows places that have changed up to 4 zone levels,a winter time low increase of 40 degrees Fahrenheit over conditions when the first hardiness zone map was issued. On the other hand the white streaks and blobs are areas where climate has not changed in 40 years and they do make up a significant percentage of the total map.