R
Ridgerunner
Guest
I don’t think these tell us very much, if anything. There are a lot of climate zone maps and they vary quite a bit. In any event, USDA (right or wrong) says they don’t tell us anything about climate change because they’re based on the lowest experienced temperatures over a period of years and because the mapping has improved over the years.There is a difference between weather and climate. Climate is the statistical aggregate of weather (over time and larger regions) and is actually impacted only by a few factors, compared to the many factors that impact weather and make it difficult to predict. Thus climate can can more easily be predicted than weather.
Another example of statistical aggregates being more easily predictable is Durkheim’s study of suicides. While one cannot predict an individual suicide, the suicide rates remain fairly constant, sometimes going up or down slightly over the years due to various factors – Durkheim’s famous factor was anomie, with which he was able to explain why suicide rates were higher in Protestant than Catholic countries, among men than women, among single than married people, among the rich than among the poor, etc.
As for climate, we have this old atlas from the 70s we picked up at a garage sale (“reuse,” a very good environmental principle), and the climate maps there are still fairly accurate. There has been a shift due to global warming, but not much – one has to look carefully.
Here is the plant hardiness zones for 1990 and 2012 – climate change has just shifted these a bit over the 22 years:
https://simpleclimate.files.wordpress.com/2012/12/merged_usda_plant_hardiness_map.jpg?w=198&h=300" srcset="https://simpleclimate.files.wordpress.com/2012/12/merged_usda_plant_hardiness_map.jpg?w=198&h=300 198w, simpleclimate.files.wordpress.com/2012/12/merged_usda_plant_hardiness_map.jpg?w=396&h=597 396w, simpleclimate.files.wordpress.com/2012/12/merged_usda_plant_hardiness_map.jpg?w=99&h=150 99w
“Because the USDA PHZM represents 30-year averages of what are essentially extreme weather events (the coldest temperature of the year), changes in zones are not reliable evidence of whether there has been global warming.
Compared with the 1990 version, zone boundaries in this edition of the map have shifted in many areas. The new PHZM is generally one half-zone warmer than the previous PHZM throughout much of the United States, as a result of a more recent averaging period (1974–1986 vs. 1976–2005). However, some of the changes in the zones are the results of the new, more sophisticated mapping methods and greater numbers of station observations used in this map, which has greatly improved accuracy, especially in mountainous regions. These changes are sometimes to a cooler, rather than warmer, zone.”
planthardiness.ars.usda.gov/PHZMWeb/AboutWhatsNew.aspx
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