U.S. media has been offering blanket coverage of the horribly destructive tornadoes that have torn through the south this month, particularly this week. Hundreds have been killed; the fatalities and ruined homes are heartbreaking.
But is this weather event unprecedented, as coverage has implied and as global warming opportunists have claimed?
The cause of this month’s tornadoes is La Nina – a cooling of the water in the tropical Pacific Ocean from the coast of South America to the International Date Line. During La Nina — and this has been a historically large one — stronger than usual jetstream winds seven miles above the Earth blow from southern California across northern Texas and to the Great Lakes. The jetstream promotes rising air and the development of strong low-pressure systems over the Great Plains, the Midwest, and the South. These strong low-pressure areas pull warm, humid air northward from the Gulf of Mexico and crash it into cool, dry air pulled south from Canada.
This scenario produces large numbers of powerful tornadoes. It has happened many times in the past.
Large numbers of deaths from these tornadoes are not unprecedented, and in fact were common before 1975. The Tri-State tornado of March 18, 1925, crossed southern Missouri, southern Illinois, and southern Indiana, killing 695 people — 234 in the town of Murphysboro, Illinois, alone.
Total deaths from tornadoes in 1925 were 800. In 1974, 319 people died, mostly on April 3. In 1965, 300 died; in 1953, 530 died; in 1936, 550 died; in 1927, 540 died; in 1917, 550 died; in 1896, 530 died.
From 1900 to 1974 an average of 250 to 300 people a year were killed by tornadoes, and in all likelihood many more would have been killed in the past had today’s population numbers existed then — many more people are in harm’s way today.
This April, nature has done what it always does in the tornado capital of the world: generate large numbers of deadly tornadoes during spring when La Nina is active. It is nothing new.
Since the mid 1970s the warning system in place to alert people to approaching tornadoes has improved, and with the advent and spread of Doppler Radars across the country in the 1990s, meteorologists are now able to see inside thunderstorms and to detect rotating circulations that can become tornadoes. This has resulted in saved lives. Since 1975 an average of about 75 people a year are killed by tornadoes, a greatly reduced total.
But even with better technology, this month was an example of how nature can overwhelm even the best warning systems. Look at what just happened in Japan, the most-prepared nation in the world for earthquakes and tsunamis.
Keep in mind that the number of total tornadoes reported will likely go down. These initial figures are of all tornado reports; many people report the same tornado. Eventually the National Weather Service will evaluate the reports and the initial reports of record numbers of tornadoes may change.
The good news: we have seen the peak of this tornado outbreak. The bad news: May is typically the peak month for tornadoes — we are not out of the woods yet.