Trends in severe weather
Politicians, and even others who should know better, have stated frequently there would be an increase in the intensity and frequency of severe storms due to global warming. But in last week’s article I showed you that the tropical storm activity across the globe is now near a 30-year low. This week, let’s take a look to see if there has been an increase in tornadoes.
According to the National Climatic Data Center, “With increased national Doppler radar coverage, increasing population, and greater attention to tornado reporting, there has been an increase in the number of tornado reports over the past several decades. This can create a misleading appearance of an increasing trend in tornado frequency. To better understand the true variability and trend in tornado frequency in the U.S., the total number of strong to violent tornadoes (EF3 to EF5 category on the Enhanced Fujita scale) can be analyzed.” For further details on this subject, visit www.ncdc.noaa.gov/oa/climate/severeweather/tornadoes.html#history.
You can see from the graph in Figure I that there was an increase in the number of strong tornadoes up until 1974, but there has been a DECREASING trend since then even though the number of people seeing and reporting tornadoes has increased. This is exactly the opposite of what has been forecast.
There have also been forecasts of increasing droughts and heavy precipitation events. I haven’t found a graphic to show this on a global scale, but the National Oceanic and Atmospheric Administration (NOAA) has compiled one for the United States.
In Figure II, the top graph shows the percentage of the United States experiencing moderate to extreme drought for each year since 1900, and the bottom graph shows the percentage experiencing moderate to extreme wet conditions.
About 80 percent of the United States was in moderate to extreme drought in the mid 1930s, but there certainly doesn’t appear to be much of an overall change in either extremely dry weather or wet weather since 1900. Going back to A.D. 1200, it appears the worst drought in North America occurred in the 1500s. According to an article in Science Daily (Feb. 8, 2000), “No other drought appears to have been as intense, prolonged and widespread as the 16th century megadrought,” and, “This drought was not a consequence of global warming. We don’t know what caused it. The factors that did cause it could return.”
Lately, even snowstorms and severe cold have been blamed on global warming, or as it is then called, “climate change.” However, a recently published article in the Journal of Climate, Dec. 2009, states, “The 1900–01 to 2006–07 trends in the annual percentage of high- and low-extreme snowfall years for the entire United States are not statistically significant.” In other words, there have been years with a lot of snowfall and years with very little, but there is no significant trend in either direction for the country as a whole since 1900.
So the next time you hear someone trying to blame a severe storm or any other type of weather event on global warming, just tell them to look at the data. These events have NOT become either more severe or more frequent, even though temperatures have become a little warmer and CO2 levels are certainly higher than at the beginning of the observational record.
Next week, I’ll take a look at how difficult it is to determine a global surface temperature. You might be surprised to learn that around 80 percent of the climate stations in the United States do not meet the published criteria for acceptable observations, and the rest of the world is even worse.
Craig James has been retired since July 1, 2008, after 40 years of broadcasting television weather. He was chief meteorologist at WZZM-TV for 12 years and chief meteorologist at WOOD-TV for 24 years. He is a graduate of Penn State University, where he received a Centennial Fellowship Award. He was also honored as a Fellow of the American Meteorological Society.