Everyone knows—or at least geniuses like Al Gore, Barbara Boxer, and John Kerry know—that
global warming climate change means more severe weather. Like Sharknados! Or at least tornadoes.
Science magazine reports on the subject this week, and since you can’t get any more 97 percenty than Science, this is worth passing along. “Increased Variability of Tornado Occurrence in the United States” finds no increase in the total number of tornadoes from 1954-2013. (See Figure 1 below.) But this is where it gets interesting: the data show a decrease in the number of days there are major tornadoes, but an increase in the number of tornadoes on the days when they do flare up. (See Figure 4 below.)
What to make of this? The authors of the study are appropriately cautious:
The fact that the two series move in opposite directions is very difficult to explain as a result of changes in how they are reported. Increased likelihood of reporting should lead to an increase in both the probability that a day has at least one (E)F1+ tornado and that a large number occurs on any particular day. It still is possible that the observed changes are the result of some nonmeteorological factors, but that would require a complex set of influences acting in opposite directions, making it exceedingly unlikely. Unfortunately, the nature of the database makes it impossible to be absolutely certain. . .
At this point, we cannot offer a physical hypothesis for the increased variability, but our analysis implies that a change in the areal distribution of favorable environmental conditions, or in the probability of a tornado given favorable environmental conditions, is involved. Determining the relative contribution will require the continued development of relationships between environments and events, which will depend on the quality of high-resolution reanalysis products of the atmosphere. How such a change would relate to the increase in global temperature, if it relates at all, is unknown at this time. (Emphasis added.)
Worth filing away the next time you hear someone assert that climate change is causing more or bigger tornadoes.