Fewer Frigid Nights in the Southeast?
According to the latest National Climate Assessment, the number of frigid nights (<32°F) will decline in the American Southeast by the 2041-2070 period due to anthropogenic climate change, and the change will be most strongly felt in the northern portion of the region.
At least that's what the climate models predict will happen over the next quarter-century.
The climate models always make things look so tidy. Smooth trends over time, homogenous and consistent trends within regions, etc. -- in other words, so unlike reality. The devil is always in the details, particularly in climate science.
Two key questions come to mind: (1) are the number of nights below freezing currently on the decline all throughout the region over the past few decades?; and (2) what is the longer-term context for frigid nights in the Southeast?
The answer to the first question is no. Only 20 of 56 climate regions (36 percent) in the Southeast show significant declines in the number of nights below 32°F since 1980, and a couple of regions show significant increasing trends. In the state that is predicted to have the greatest decline in number of freezing nights -- Kentucky -- there are no significant trends over the past three-and-a-half decades. That seems to be a problem for the climate modeling predictions.
But that isn't the real story from a good historical look at the number of freezing nights in the Southeast. When we examine the available continuous record in each region -- which dates back as far as the 1870s, nearly half the areas (25 out of 56) have significant increasing trends over time. For about half the southeast, the long-term view is that the current number of freezing nights is much higher than it was a century or more ago.
In the 1900s and 1910s, Lynchburg, VA averaged 75 nights below freezing. Since 2000, the annual average is 93. In Little Rock, AR the average has moved up from 38 to 47 over the past century.
Overall, the Southeast only has a minority of its region showing any significant trends towards fewer freezing nights since 1980, whereas nearly half the sites show an overall trend toward more -- not less -- nights below 32°F over their entire historical records, and much of the region still currently experiences more freezing nights than it did a century or more ago.