In article says...
http://arborday.org/media/zones.cfm

The new map looks close to the 1960 map.
http://www.b-and-t-world-seeds.com/Usa_zone.htm

Not really. The new map puts Chicago extremely close to zone 6 and the
1960 map looks like the 1990 map. I realize global warming is probably
not a good thing but I don't mind being upzoned without having to move.