Weather experts disagree on effect of climate change, severity of tornadoes

Is it possible that weather researchers in the future will look back on the 2011 tornado that struck Joplin and identify it as the beginning of a trend of more violent tornadoes brought on by climate change?

Some climatologists believe climate change is having an impact on the severity of storms and not just in the Midwest, but around the globe.

But others think natural variability and the conditions of the moment are the culprit, arguing that there is nothing new about severe storms, severe droughts and torrential rains.

The issue is a hot one among weather scientists, but a look at the 60-year history of the frequency and severity of tornadoes in Northeast Oklahoma, Southwest Missouri and Southeast Kansas indicates something might have changed.

In the span of 11 years, six powerful tornadoes — all F3 or greater — have killed 201 people, injured more than 1,600 others and caused property losses in the billions of dollars.

• On April 19, 2000, an F3 tornado ripped across Parsons, Kan., damaging or destroying more than 920 structures. No one was killed and few people were injured.

• On May 4, 2003, an F3 tornado slammed Pierce City. A second F3 hit Carl Junction. A third tornado, an F4, leveled Franklin, Kan., before traveling to Stockton. Nineteen people were killed and scores were injured. Thousands of structures were destroyed.

• On May 10, 2008, an EF-4 tornado tore across Picher, Okla., and then Newton County, Mo., killing 21 people and injuring 353 others. Hundreds more homes, businesses and other buildings were damaged or destroyed.

• On May 22, 2011, an EF-5 tornado roared across Joplin and Duquesne, killing 161 people and injuring more than 1,150. Nearly 8,500 residential and business structures were damaged or destroyed.

(In 2007, the National Weather Service replaced the Fujita Scale with the Enhanced Fujita Scale, hence the addition of the letter “E” in describing the severity of tornadoes.)

That’s six tornadoes of F3 or greater since 2000, compared with eight F3 tornadoes and two F4 tornadoes in the previous 50 years combined for the same counties in the Tri-State Area, according to weather records maintained by the National Weather Service. There was no F5 tornado in the region until 2011.

And until the 2003 outbreak, deaths from tornadoes were limited to generally one or two or a handful of residents per storm. But the 2003, 2008 and 2011 tornadoes each resulted in more deaths in the region than all of the deaths recorded from 1950 to 2000 combined.

Warmer GULF

Six severe tornadoes in 11 years could be a natural anomaly, but Kevin Trenberth, senior scientist at the U.S. National Center for Atmospheric Research’s Climate Analysis Section in Boulder, Colo., has a different theory.

“There is climate change going on,’’ he said. “The oceans are now 1 degree Fahrenheit warmer than they were, and that includes the Gulf of Mexico. The warm and moist air coming out of the Gulf plays a key role.’’

Severe tornadoes are generated by supercell thunderstorms that form when cold air collides with warm, moist air. An active jet stream provides the wind shear needed to create rotation.

“This warm and moist air leads to more instability in the atmosphere, and stronger thunderstorms and heavier rains. It sets the stage for the supercells that create the environment for tornadoes,’’ he said.

“You also need wind shear. You have plenty of wind shear in spring time with the jet stream barreling across the country. It’s a chain of things that come together.’’

Trenberth said the 1-degree increase in the temperature of the water in the Gulf of Mexico since the 1970s translates into a 4 percent increase in the amount of water vapor in the air that streams northward from the Gulf into the Midwest. That increase in moisture creates greater instability in the atmosphere.

“Moisture is fundamental to the formation of a supercell. The water vapor in it expands and cools to produce rain,’’ he said. “This increase in warm and moist air changes the odds that a supercell storm will form. That’s the climate change connection.

“I think a case can already be made that there is an influence and that it is only apt to grow in time.’’

Trenberth said that nationwide there are more tornadoes being reported, but whether there are actually more storms as a result of climate change, or whether that is a result of improved detection, hasn’t been determined.

“There has generally been an increase in the record, but that’s because more people in more places are seeing them. And, our ability to detect them with radar has improved over time, especially in the late 1980s when Doppler radar increased our capabilities of detecting them,’’ Trenberth said.

“The best evidence that climate change is affecting our weather is not from tornadoes, but from rainfall statistics that go back over 100 years. It’s raining harder than it used to because there is more water vapor in the air.’’

A study by the Water Resource Center of the Missouri Department of Natural Resources shows that rainfall in Joplin has increased from about 35 inches a year in 1950 to nearly 50 inches a year in 2000.

‘Insufficient data’

Howard “Howie’’ Bluestein, a professor of meteorology at the University of Oklahoma since 1976, is familiar with Trenberth. In fact, they have discussed climate change and severe weather over dinner more than once.

But Bluestein — a key participant in the VORTEX tornado-research projects and inventor of TOTO, a tornado-measuring device that inspired the fictional “Dorothy’’ in the movie “Twister” — does not concur with Trenberth’s assessment.

“My take is that we absolutely do not know whether tornadoes are becoming more intense or more frequent because of climate change,’’ he said. “It’s possible that we could look back on last year’s storms and say they were the beginning of a trend, but we need about another 100 years or more of weather to know whether that is true.

“There have been powerful tornadoes in the past that have gone through populated areas,’’ he said.

Large F5 tornadoes in the 1950s hit Waco, Texas, and Flint, Mich., and each killed more than 100 people.

The Tri-State Area has had some big tornadoes in the past, too. On April 3, 1956, an F4 tornado traveled from Ottawa County, Okla., through Cherokee County, Kan., into Jasper County, Mo. It injured 54 people. It would be 55 years before another tornado as powerful would hit Jasper County. That was on May 22, 2011.

The other F4 struck on April 25, 1975, in Newton County, killing three people.

Bluestein’s position is supported by a report released after last year’s severe tornadoes by EQECAT Inc., which provides catastrophic modeling services to the global property and casualty insurance, reinsurance and financial markets.

EQECAT said a strong jet stream was positioned over “tornado alley’’ in the spring of 2011 and that contributed to favorable conditions for convective storms and the creation of six EF-5 tornadoes that year in Missouri, Oklahoma, Mississippi and Alabama.

The report states that the level of tornado activity in 2011 cannot readily be associated with climate change and that a review of tornado observation data does not identify any ongoing trend associated with temperature change.

The report states: “The year 2011 is an exceptional year with six EF-5 tornadoes, but seven EF-5 tornadoes in 1974 demonstrate that this level of extreme events is not unseen. There is insufficient data to conclude that we are in the midst of a new trend.’’

Bluestein concedes that climate change is happening and that it is putting more water vapor in the air.

“Global warming is happening. The amount of water vapor in the air will increase with that. It’s something that you need to make the clouds for these storms,’’ he said. “But you also need vertical wind shear. How will that change in a global warming scenario is absolutely unknown.

“It might be that wind shear decreases or causes regional changes. It could create stronger shear in some areas and weaker shear in other places,’’ he said. “We absolutely don’t know that for certain.’’

Bluestein said more research needs to be done before any conclusion can be drawn.

Said Bluestein: “I might be a believer after 50 to 100 years when the number of tornadoes and their intensity are indisputable. But for now, it’s an unknown.’’

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