Climate Spinning Stronger Tornadoes Across US?
NASA Earth Observatory image created by Robert Simmon, using data provided courtesy of NASA/GSFC/METI/ERSDAC/JAROS, and the U.S./Japan ASTER Science Team
The damage scar left by the EF5 tornado that struck Moore, Okla., on May 20, 2013, as seen by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite on June 2, 2013.
Deadly tornadoes have lashed the United States for centuries. Most of the worst occurred before modern warning systems existed, although one occurred almost exactly two years before the deadly twister that struck Oklahoma on May 20.
The deadliest tornado in U.S. history, the Tri-State Tornado of March 18, 1925, ravaged 219 continuous miles of Missouri, Illinois and Indiana. Nearly 700 people lost their lives in that single tornado, according to NOAA. However the twister was not officially classified by NOAA as an EF5 -- the most damaging type -- because of a lack of data, nor were there official records of wind speeds.
On May 22, 2011, the deadliest tornado yet recorded by the new Enhanced Fulita Scale struck Joplin and killed 158 Americans, making it the seventh deadliest in U.S. history. Winds exceeded 200 miles per hour as the EF5 tornado demolished a path that was 22.1 miles long and up to 1 mile wide.
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The second deadliest tornado in U.S. history whipped along the Mississippi River on May 2, 1840, ending 317 lives, according to NOAA’s Storm Prediction Center. The tornado killed hundreds on boats and barges on the river until striking Natchez, where the storm killed dozens more. Like all tornadoes from before 1950, NOAA lacks sufficient data to classify the Natchez tornado as F5 or EF5.
St. Louis, Mo.
St. Louis suffered a tornado’s wrath on May 27, 1896, when at least 255 people died. A study published in Weather and Forecasting estimated that the tornado cost $2.2-$2.9 billion in 1997 dollars when adjusted for inflation and wealth increases, making it the costliest tornado in American history. The death toll made it the third deadliest.
On April 5, 1936, the fourth deadliest tornado in U.S. history struck Tupelo, Miss., and killed 216. A total of 436 people died in the outbreak of 17 tornadoes that included the Tupelo twister. Tetsuya Fujita of the University of Chicago and Tom Grazulis, head of the Tornado Project, retroactively rated the Tupelo tornado as an F5 on the scale invented by Fujita.
The same storm system that lashed Mississippi in 1936 continued on to Georgia where it unleashed the fifth deadliest tornado in U.S. history and killed 203 people in Gainesville. Fujita and Grazulis rated this tornado an F4, meaning winds reached 207-260 miles per hour.
Oklahoma is no stranger to tornadoes. The sixth deadliest on record struck on April 9, 1947. The storm nearly destroyed the towns of Higgins and Glazier. In Woodward, Okla., 100 city blocks were destroyed and 107 lives lost, according to the Tornado Project. A total of 181 people died in the tornado.
The largest outbreak of F5 super-tornadoes occurred April 3-4, 1974. Seven F5 tornadoes struck in a single 24-hour period. In total, 147 tornadoes whirled through the central portion of the United States on that day.
On May 22, 2004, the largest tornado ever recorded hit Hallum, Neb. The twister stretched nearly 2 1/2 miles across. No one died in the massive twister.
Groups of tornadoes or outbreaks can cause as much or more damage than a single giant storm. The “Dixie Outbreak” of April 27, 2011, killed 316 people according to NOAA’s Storm Prediction Center. More Americans died in tornadoes that day than any other in this century.
SAN FRANCISCO — The trail of twisted metal and torn roofs left behind by massive twisters is growing longer and wider, a sign that tornadoes may be growing stronger, climate scientist James Elsner said here Tuesday (Dec. 10) at the annual meeting of the American Geophysical Union.
Beginning in 2000, tornado intensity — as measured by a twister's damage path — started rising sharply, said Elsner, of Florida State University. "I'm not saying this is climate change, but I do think there is a climate effect," he said. "I do think you can connect the dots."
Devastating tornado outbreaks in recent years, such as the massive storm that injured hundreds in Moore, Okla., this summer, have focused attention on whether climate change is altering tornado frequency and strength. Just last week, a heated debate played out in an op-ed on LiveScience and the New York Times over whether tornado-tracking data could answer these questions. One scientist claimed the data show twister numbers are dropping, but tornado experts said changes over time in how weather officials assess tornado size and damage make it difficult to look for climate patterns. [Gallery: Moore Tornado Damage]
But Elsner said tornado data are good enough to reveal whether global warming is altering twisters. "I've been working with hurricane tracking data for 25 years, and tornado tracking data is better," Elsner said. "We have the tools, we have the data to answer the question. Statisticians drool when they see stuff like this."
"I think we're at the point where we were 30 years ago with hurricanes. People were skeptical about the connection between hurricane and climate, but now they don't even blink," he said.
Elsner is the first to admit he doesn't have the climate answers, but he said his early results are a step in the right direction: finding a way to solve the data conundrum.
Elsner's solution was to drop the human factor. Instead, he looked at wind speed and the size of the damage path (its length and width) to gauge whether tornado intensity has changed since 1994. (The United States has been almost completely covered by Doppler weather radar since 1994.) Using the damage path to gauge intensity avoids problems such as analyzing tornado strength via the Fujita and Enhanced Fujita scales, which are based on observations by weather service officials, he said.
Elsner analyzed damage paths and wind speeds using a statistical model. The result: a sharp upward spike starting in 2000. He also looked at earlier data, since the 1970s, which showed a much slower rise.
Puzzling out how climate change alters tornadoes is the big next step, Elsner said. One way this could happen is by adding moisture (via humidity) to fuel storms in Tornado Alley, the storm belt where tornadoes spin up in the United States. Warmer air holds more moisture. But Elsner said it was also important to track tornadoes in Canada, because there are hints that big ridges and troughs in the jet stream's powerful winds could be triggering more tornadoes up north, and fewer in the United States.
"We really need a North American data set to answer questions about frequency," he said.
Original article on LiveScience.
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