Although the number of major tornadoes has increased over the last 50 years, there is no statistically significant trend.

By definition, if there is "no statistically significant trend," then you cannot say that "the number of major tornadoes has increased over the last 50 years." A lack of statistical significance means that the null hypothesis (i.e., no change in tornado frequency) cannot be rejected. Thus, the scientifically correct way this sentence in the NCA should have been written is as follows: there has been no statistically significant trend in the number of major tornadoes over the last 50 years. Full stop. Nothing more, nothing less.

But the following plot encapsulates the key concerns over the NCA's alarmism.

Click the image to enlarge.

The figure shows the "projected average number of days per year with maximum temperatures above 95°F for 2041-2070 compared to 1971-2000, with the lower left figure showing the historical (aka 1971-2000) number of days per year with maximum temperatures above 95°F and the plot in the lower right showing the projected number of days of this extreme heat by the 2041-2070 timeframe.

Note the differences between the historical and projected climate. Almost all of Florida is predicted to move from having somewhere between 0-15 days >95°F at present up to more than 75 days per year at >95°F. As I understand this plot, the difference between the values on the lower right figure minus the values on the lower left figure should equal the values on the upper plot, but they don't. Just take Florida. The lower right plot shows almost all of Florida as having >75 days of extreme heat. The lower left plot shows almost all of Florida having between 0 and 15 days of extreme heat. The difference is therefore somewhere between 60 and 75 days. Now look at the upper plot; most of Florida is colored with less than a 50-day change, whereas it should be almost entirely colored with a >60-day change. Who knows what is going on? And the NCA certainly doesn't take the time to explain the obvious discrepancy between what it says it is showing in its figures and what the figures themselves actually show.

Regardless, I'm going to focus on the two lower plots, and see how reasonable (or unreasonable, as the case may be) those massive predicted increases in numbers of extreme heat days throughout much of the American Southeast appear to be. The following table shows the average number of days per year with maximum temperatures above 95°F between 1980 and 2013 for the various climate sub-regions throughout the Southeast, along with whether any of the trends are significant.



Click the image to enlarge.

Out of the 54 regions, only three have significantly increasing trends (~4 days/decade) since 1980. Fort Myers, Florida has a significantly decreasing trend of ~3 days/decade. The other 50 regions (i.e., 93%) have no significant trends in the number of extreme hot days per year over the past three and a half decades. But somehow we are to achieve enormous increases in the number of very hot days across most of the Southeast over the next three decades?

To show how ridiculously large these NCA projections appear to be, have a look at the graph below. It shows the historical number of days per year with maximum temperatures above 95°F between 1940 and 2013 for the Miami area in Florida, along with the 1980-2013 average (1.5 days/year), and the NCA's projection of this region moving to a new "normal" of >75 days/year.

So there has been no significant trend in the number of extremely hot days in the Miami area since at least 1940, and certainly not since 1980, and yet we should expect to see a more than 50-fold (i.e., >5,000%) increase in the number of extreme hot days over the next 30 years?

Nothing to see here; everybody just move along, and don't question the NCA lest you be labeled a "climate denier" not willing to accept "settled science."

These topics are not trivial, either. Not only is the generic climate science in the NCA being used to support efforts to radically restructure the nature of the global economy and the relationship between its citizens and their property and their respective governments, but expensive infrastructure planning in the American Southeast is apparently also being based on these types of projections. The stakes are very high, and the problematic science in the NCA needs to be repeatedly brought forward into the public sphere.