|John Christy on US-tornadoes12-11-2013 22:02|
|Dr. John Christy has in his presentation to Climate Change Roundtable from 30th May 2013 showed a graph with the evolution of the number of tornadoes by years.|
This graph is part of his internet presentation with a mixed panel (pro and con AGW). The panel who were quizzed on climate change by Rep David McKinley, a Republican congressman from the coal state of West Virginia consisted of:
Scott Denning...........Colorado State University
Jim Hurrell................National Center for Atmospheric Research
Joe Casola................Center for Climate and Energy Solutions
Annie Petsonk...........Environmental Defense Fund
Richard Thomas.........West Virginia University
Marc Morano..............Climate Depot
Dennis Avery.............Hudson Institute
Myron Ebell...............Competitive Enterprise Institute
Without any statistical analysis it looks like the number of tornadoes is fairly constant over the years 1954-2012.
What can you say about the development in the number of tornadoes in the U.S.?
In general, it is believed that there will be a deceasing trend in number of tornadoes with an increasing global temperature. In order to generate a tornado, hot and humid air must be present and in addition to this, there must be a strong wind shear. In a world with higher temperature the first will be present while wind shear will diminish. So there are opposing factors, but the net result is expected to be a decrease in the number of tornadoes.
The development of the number of tornadoes in the United States is very well described with comprehensive statistics. However, it is difficul to use this material historically, since data recording has been improved and changes in the classifications of tornadoes have taken place over the years. This is one of IPCC's main arguments for not taking a clear stance on trends of tornadoes.
Has there been a Change in Extreme Events like Heat Waves, Droughts, Floods and Hurricanes?
Observational evidence for changes in small-scale severe weather phenomena (such as tornadoes, hail and thunderstorms) is mostly local and too scattered to draw general conclusions; increases in many areas arise because of increased public awareness and improved efforts to collect reports of these phenomena.
From the following section I have copied:
22.214.171.124 Tornadoes, Hail, Thunderstorms, Dust Storms and Other Severe Local Weather
Evidence for changes in the number or intensity of tornadoes relies entirely on local reports. In the USA, databases for tornado reporting are well established, although changes in procedures for evaluating the intensity of tornadoes introduced significant discontinuities in the record. In particular, the apparent decrease in strong tornadoes in the USA from the early period of the official record (1950s–1970s) to the more recent period is, in large part, a result of the way damage from the earlier events was evaluated. Trapp et al. (2005) also questioned the completeness of the tornado record and argued that about 12% of squall-line tornadoes remain unreported. In many European countries, the number of tornado reports has increased considerably over the last decade (Snow, 2003), leading to a much higher estimate of tornado activity (Dotzek, 2003). Bissolli et al. (2007) showed that the increase in Germany between 1950 and 2003 mainly concerns weak tornadoes (F0 and F1 on the Fujita scale), thus paralleling the evolution of tornado reports in the USA after 1950 (see, e.g., Dotzek et al., 2005) and making it likely that the increase in reports in Europe is at least dominated (if not solely caused) by enhanced detection and reporting efficiency.
These quotes should stop all discussions about the development of tornadoes in the US for the time being. However, I would like to verify this myself by using data from NASA storm prediction Center.
I order to check this conclusion, I have used a generalized linear model to examined the to development in the number of tornadoes in the US. The results are shown in the following graph:
Information about tornadoes of types 0, 1 and 2 is not reliable due to improved recording of data and changes in classification. Therefore, the growth of these types of tornadoes has nothing to do with global warming.
By contrast the number of tornadoes of type 3, 4 and 5 seems to be reliable due to good recording of these type of tornadoes throughout the years from 1950 to 2012.
Based on this model, it appears that the number of tornadoes of types 3 and 4 are significantly decreasing, while the number of tornadoes of type 5 also is decreasing, but not significantly.
All in all, the number of tornadoes of types 3, 4 and 5 is in line with what the theory of global warming indicates.
In comparison, I have plotted the same data, but with a trend curve included using a generalized linear model. This model indicates that there is a significant decreasing trend.
The above graph shows that the number of tornadoes of types 3, 4 and 5 is decreasing.
There is a clear indication that the number of severe tornados are decreasing i US.
This is in line with the theory of global warming.
Christy has not given the full picture about the tornado development in US.
Christy has all resources to find and read IPCC reports on the development of tornadoes in the US. It surprises me that he does not appear to give the complete picture on tornadoes in the US. This is disappointing: He owes us a better effort.
I would like to thank Christy for the discussion of the US tornado statistics hoping that in future he will give a more balanced presentation of US tornado statistics.
Edited on 12-11-2013 22:06
| The Real Truth About Tornadoes (Op-Ed)|
This open letter was written by six, leading tornado experts from research institutions across the United States. Their brief bios follow below. The authors contributed this article to LiveScience's Expert Voices: Op-Ed & Insights.
Is Climate Change Causing the Record-Breaking Tornadoes & Floods?
Already this year, nearly 1,200 tornadoes have crisscrossed Tornado Alley, killing nearly 500 people and leaving thousands more homeless. Meanwhile, twice as much rain fell in several states in the Ohio Valley this April than during any other April on record. It produced extreme floods in May, swelling the Mississippi River to a record depth of 60 feet.
Edited on 07-12-2013 12:33
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