The map is used by gardeners to select plants that are best suited to the local climate, as described by temperature range. This is the first revision since 1990. Although it is not a guide to climate change as such it does show some area of significant changes over the last 20 years.
As described in USA Today, the changes are not dramatic with none over a half a zone. Most of the changes show a warming to the north. In the words of gardening consultant Charlie Nardozzi:
"If you want to look at what might be the most politically correct thing, you can say something's happening. But the climate is changing. Spring is coming sooner and lasting longer. Fall lasts longer, and overall the weather is so much more erratic now."While these designations are accurate generalizations, local landscape can make a difference which the map cannot describe. Our Bull Creek valley runs north-south with fairly steep sides. The sun hits it late and goes down early behind the hills. The evening temperatures are between 5-10 degrees cooler than the surrounding uplands.
Meanwhile, Matt Ridley has an interesting take in his Wall Street Journal article,
Are We Holding a New Ice Age at Bay? He points out that even considering the Little Ice Age (1550-1850) our 10,000 years of developing civilization has occurred in an unusually warm spell. Temperatures like ours have occurred in less than 10% of the time over the last one million years. Indeed, one theory is that the unusual warmth allowed our predecessors to develop agriculture, the first step in civilization.
He discusses some of the hot and cold history of our planet and the theory of some that the current warming may be postponing the next ice age. Before you run out and buy a heavier coat, note that experts are talking about the next 1500 years. As with all climate theory, it is interesting but nothing to hang that heavy coat on.