My sister pointed out to me that the USDA has updated the plant zone hardiness map. In many areas, zones have changed reflecting warmer climates. I am just north west of Boston and was in zone 6a. Now I am squarely in zone 6b. This means there has been a 5*F change in minimum average extreme winter temperature. Up from -10* (in the last USDA version released in 1990) to -5* (the average from 1976 to 2005) in the map released a couple days ago.
A couple of links are here:
Plant zone maps at the USDA Agricultural Research Service and
An article at The Salt, NPR