This is sparked by a discussion I saw in another diary, in which the claim was made that no studies have shown any evidence that increased tornado activity is a consequence of climate change. And it is true that scientists lack the means to prove that any specific outbreak of tornadoes is the result of anthropogenic climate change (primarily as the result of increased levels of CO2 in the atmosphere die to the use of fossil fuels. That said, recent studies have begun to show that, as climate scientists have long hypothesized, there is evidence that shows increased severe precipitation events such as we have seen this spring - a known consequence of rising temperatures - very well may be responsible for an increase in the number and intensity of tornado outbreaks.
Dr. Kevin Trenberth, the former head of the Climate Analysis Section of the National Center for Atmospheric Research, emailed me that “the study is plausible.” Both Trenberth and another top climatologist, Dr. Michael Mann, agree that:
This latest study [Elsner, j., Elsner, S., and Jagger, T. (2014) The increasing efficiency of tornado days in the United States, Climate Dynamics] provides further evidence for what many climate scientists have already surmised: that climate change is substantially altering the atmospheric environment in which thunderstorms and tornadoes form, increasing risk of major tornado outbreaks when conditions are ripe.
Mann adds, “The findings, moreover, undermine the claim made by some contrarians that human-caused climate change will reduce tornado activity and risk.”
The
authors of the aforementioned study include its lead author, James Eisner, who is a professor of Geography at Florida State University a/k/a FSU, has previously published numerous research papers on hurricane and tornado activity and is listed as
"an expert on climate and weather, and in developing statistical models for predicting severe weather activity such as hurricanes and tornados" on FSU's website.
Thomas Jagger, who has
authored or co-authored a number of papers in the area of Climatology, holds a Ph.D. in statistics and is a former research associate at FSU. Svetoslava C. Elsner is a meteorologist. So, what did their
study show exactly? From the abstract:
The authors analyze the historical record of tornado reports in the United States and find evidence for changes in tornado climatology possibly related to global warming. They do this by examining the annual number of days with many tornadoes and the ratio of these days to days with at least one tornado and by examining the annual proportion of tornadoes occurring on days with many tornadoes. Additional evidence of a changing tornado climate is presented by considering tornadoes in geographic clusters and by analyzing the density of tornadoes within the clusters. There is a consistent decrease in the number of days with at least one tornado at the same time as an increase in the number of days with many tornadoes. These changes are interpreted as an increasing proportion of tornadoes occurring on days with many tornadoes. Coincident with these temporal changes are increases in tornado density as defined by the number of tornadoes per area. Trends are insensitive to the begin year of the analysis. The bottom line is that the risk of big tornado days featuring densely concentrated tornado outbreaks is on the rise. The results are broadly consistent with numerical modeling studies that project increases in convective energy within the tornado environment.
In effect, what they found was that while the mean number of tornadoes per year has not shown an increase, the density and severity of tornado outbreaks is on the rise. In other words, we are seeing more days with multiple tornadoes, which are also more highly concentrated geographically. From the
press release issued by FSU regarding this research:
New research by a Florida State University geography professor shows that climate change may be playing a key role in the strength and frequency of tornadoes hitting the United States.
... Professor James Elsner writes that though tornadoes are forming fewer days per year, they are forming at a greater density and strength than ever before. So, for example, instead of one or two forming on a given day in an area, there might be three or four occurring.
"We may be less threatened by tornadoes on a day-to-day basis, but when they do come, they come like there's no tomorrow," Elsner said.
Elsner, an expert in climate and weather trends, said in the past, many researchers dismissed the impact of climate change on tornadoes because there was no distinct pattern in the number of tornado days per year. In 1971, there were 187 tornado days, but in 2013 there were only 79 days with tornadoes.
But a deeper dive into the data showed more severity in the types of storms and that more were happening on a given day than in previous years.
Eisner, Eisner, & Jagger's study is consistent with a
2013 paper by Stanford climate reseachers, which found " robust increases in the occurrence of severe thunderstorm environments over the eastern United States," which they suggested would lead to "a possible increase in the number of days supportive of tornadic storms." It is interesting to note that insured losses (not total damages) from extreme thunderstorms and tornadoes
exceeded $10 Billion (in 2014 dollars) for each of the years from 2008 - 2014, with total losses for those years ranging from a low of around $15 Billion (2013) to a high just short of $50 Billion (2011). From 1980 - 2008 there were only six years in which total losses from storm and tornadoes exceeded 10 Billion.
While not conclusive, this data strongly suggests that a warming climate is changing both the pattern and destructiveness of tornado outbreaks in the United States, and, as James Eisner himself points out, these effects from climate change are not just related to tornadoes. It includes both droughts and flash flooding as well.
[T]he nature of tornado activity does seem to be changing. Elsner’s study found that, though the total number of tornadoes has remained constant, they are occurring on fewer days and arriving in larger clusters — which can mean longer, more powerful tornadoes with greater potential for destruction.
A super cell thunderstorm can create a single tornado that lasts anywhere from a few minutes to 20 or 30 minutes, on average. But as that storm continues to move downwind, it can produce additional tornadoes an hour or two later. This type of clustered tornado activity is happening more regularly, Elsner says, and the clusters appear to be growing larger. [...]
It’s not just tornadoes.
In the South Central US and Mexico, entire regions went from dry and arid conditions to flood in a matter of hours. “We know that both of those extremes, in terms of drought and in terms of extreme precipitation, have been linked to climate change,” says Andrew Freedman, Science Editor of Mashable.
It’s right to think that extreme weather is off the charts. Climate changes is certainly linked to such events.
Although climate patterns such as the extremely strong
ENSO (El Nino Southern Oscillation) clearly has a lot to do with our weather this year, the increase in energy absorbed by the earth's oceans as a result of increased in the concentration of greenhouse gases in the earth's atmosphere
played a significant role in the formation of the "super El Nino" that is causing such devastating weather this year. Consider global warming induced by these greenhouse gas emissions as analogous to gasoline being poured onto an existing fire. That, in essence, is what we are doing.
And by doing so, we increase the risk of severe weather of all kinds - drought, severe storms with flooding, tornadoes and heavier than normal snows in winter, depending on your location, and other climate variables, such as the aforementioned El Nino. The sooner we acknowledge that these extreme weather events are a consequence of our behavior in altering the earths' climate through warming, the sooner we can do something about the dangers that changing climate poses to all life. We have existing technologies in place - solar, wind, geothermal and energy conservation measures - that are available to wean us from our addiction to the fossil fuels. All we need is the will to act.
