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Stop The Presses! The Headlines are Wrong!
Have you heard that the United States Department of Agriculture has released a new plant hardiness zone map for the United States? You may have heard that this map indicates global climate warming.
Does the new USDA map offer proof that the climate is warming? No, it does not. Is the climate changing? Of course it is — it always has been and hopefully always will be. The 2012 USDA map does not represent the new norm for climate.
The USDA website notes: "Climate changes are usually based on trends in overall average temperatures recorded over 50-100 years. Because the (new map) represents 30-year averages of what are essentially extreme weather events (the coldest temperature of the year), changes in map zones are not reliable evidence of whether there has been global warming."
Anyone who says that the new map indicates global warming is either uninformed or is pushing an agenda. Short-term weather is not the same thing as climate, and measuring only one aspect for only a few decades is not reliable.
There have been cold hardiness zone maps since Alfred Rehder published one in 1927. In 1960, 1965 and 1990, the USDA produced maps. Each map update used more recent temperature data rather than adding to the existing data to create a longer-term map.
The 1990 USDA map looked at 14,500 locations but used only 8,000 weather stations that had valid data, which was twice as many as the previous maps. The 1990 USDA map used the average minimum temperature for the 13 years between 1974 and 1986. The 1990 map showed much of the country as being a zone or more colder than the 1965 USDA map. The 1965 map used data from a short warmer period of years, and the 1990 map used data from a short colder range of years.
The Arbor Day Foundation (ADF) released a new map in 2006 using data from only 5,000 stations during the previous 15 years, which were back to being warmer, so their short-term map once again looks a lot like the 1965 USDA map. Since we have weather data from many more weather stations and longer times, it makes no sense to create a map from such limited data.
The 2006 ADF and 2012 USDA maps cannot be touted as showing proof of global warming, just as the 1990 USDA map didn't show global cooling. Average weather is made up of highs and lows. Taking a small sampling of data will most likely taint the data to one end or the other. If we did maps one year at a time, sometimes we would have very warm maps and sometimes very cold ones. The trees and shrubs for which most people use the zone maps live far longer than a decade or two, so maps developed from short-term data can be misleading to gardeners.
The methodology used to analyze the data for the 2012 USDA map is different from all previous maps, so they're not easily comparable, even though the resulting maps look similar. The current researchers used an algorithm in an attempt to increase the accuracy of their limited data. They used the formula to fill in areas of the map like mountainous regions where less data existed. For the first time in hardiness zone mapping, they asked local experts to help the researchers consider such factors as changes in elevation, nearness to large bodies of water and position on the terrain, such as valley bottoms and ridge tops. Whether or not they did increase the accuracy will be looked at by other researchers in the future.
The current researchers will publish their results and methodology in peer-reviewed journals for other scientists to evaluate. That's what good scientists do. They publish their work and let other scientists look at the methodology used and the results developed. The other scientists may refute it or may develop ways to increase its accuracy. To declare any research finished is to preemptively refute the scientific work of future scientists. Claiming that any scientific work is complete, irrefutable and cannot be challenged, is completely unscientific. Will this new map hold up to scrutiny or will it be revised? Only time will tell.
Next week, we'll look at how much influence a cold hardiness map should have on a gardener's choice in plant material.
Email questions to Jeff Rugg at email@example.com. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.
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