Rethinking the New Plant Hardiness Zone Map The USDA map released earlier this year is out of date. While the planet average is only 0.8 degrees C warmer, US Winter temperatures are 2 degrees above preindustrial levels. Nir Krakauer, an assistant professor of civil engineering at the Grove School of Engineering at City College of New York, has overhauled the U.S.D.A.’s hardiness map to better acc…