Generating Some Heat

Many observers say the new growing zones map is further evidence of climate change. The USDA says the map alone can’t prove it.

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USDA Plant Hardiness Zones

USDA Plant Hardiness Zones

Earlier this year, the USDA released a new map of U.S. growing zones created with more sophisticated and extensive data than previous versions. The map replaces a version that was released in 1990.

The new map relies on data from some 8,000 weather stations and takes into account elevation, topography, prevailing winds, proximity to large water bodies and other factors not used to create the previous version. Perhaps the biggest change is that the map shows winters are getting warmer across the country.

Used by gardeners, plant wholesalers, crop insurers and farmers to determine what areas of the country are too warm or cold for particular plants, the map has already generated some heat of its own. Many observers say the map is further evidence of climate change. The USDA says the map alone can’t prove it.

The controversy is similar to that surrounding a now-retracted growing zone map released in 2003. After environmentalists and casual observers alike pointed to it being proof of man-made climate change, it was pulled by the agriculture department, which said the methodology used to create it was outdated.

According to a story in Wall Street Journal, the warmer winters are allowing cotton to be grown in Kansas, and the Midwest corn-growing region to expand north and west into South and North Dakota, as well as into Manitoba.