most of the US has become a half zone () hotter in winter compared to the 1990 release. Research in 2016 suggests that USDA plant hardiness zones will shift even further northward under climate change. See also Agriculture Gardening Geographical zone Hardiness (plants) Subtropics References Bibliography External links Freeze/Frost data from NOAA Data on plant hardiness in Ireland Plant Hardiness Data (Canada) Plant Hardiness Zones of Canada – Interactive Map Agricultural terminology Horticulture Climate zones Geographic classifications