Are tornadoes environmental disasters?

Illuminating answers to environmental questions.
May 23 2011 12:32 PM

Are Tornadoes Environmental Disasters?

Not compared to hurricanes.

Tornado damage
Tornado damage

The 2011 tornado season has been particularly intense, killing more than 450 people and destroying untold millions of dollars worth of property. The tornado that ripped through Joplin, Mo., on Sunday, killed at least 89 people and left a six-mile wide swath of destruction. But are tornadoes also environmental disasters?

Not really. Tornadoes showcase nature's raw power, and they make great television. But in the grand scheme of environmental threats—global warming, say, or agricultural runoff and algal blooms—they barely register.

Consider their size. The average tornado is a mere 200 feet to 500 feet in diameter, and runs its course in just 1,500 feet. The biggest storms can leave tracks a mile wide, and travel more than 30 miles on the ground. (There's rarely noticeable damage more than a mile outside a tornado's direct path.) Compare that to hurricanes, which average 300 miles across (PDF), for a total directly hit area of more than 70,000 square miles at a given moment. America's largest forest fires have incinerated more than 4,000 square miles of land. The 2011 tsunami flooded 181 square miles in Japan. Earthquakes have damaged buildings across 50,000 square miles.

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Tornadoes are also relative weaklings. A tornado usually unleashes around 10,000 kilowatt-hours of energy—equivalent to 9 tons of TNT. A hurricane weighs in at around 10 billion kilowatt-hours. A magnitude 9 earthquake releases more than 550 billion kilowatt-hours of energy—the equivalent of 475 million tons of TNT or 25,000 nuclear bombs.

While tornadoes carry relatively little total power, their energy is concentrated in a very small area. As a result, if a tornado struck a particularly sensitive region, it could deal some serious environmental damage. Fortunately, "tornado alley" in the United States, where one-quarter of the country's largest tornadoes strike, isn't exactly a coral reef. It includes parts of Colorado, Kansas, Nebraska, Oklahoma, South Dakota, and Texas. Sure, there are 16 endangered species living in those states—such as the adorably named robust cottontail rabbit—but the area is considered a low priority by conservationists. In fact, Conservation International has identified only one "biodiversity hotspot" in the entire United States, the California Floristic Province along the West Coast. Only two moderately strong tornadoes have occurred in California since 1950, causing zero human deaths. (Tornado distribution isn't set in stone: A 2008 study suggested that global climate change might increase the frequency of tornado-friendly conditions in certain parts of the world, including the southeastern United States)

Hurricanes pose a far greater threat to biodiversity than twisters do. Much of the Caribbean has been declared an environmentally sensitive area; 50 percent of its plants and 46 percent of its mammals exist nowhere else on Earth. Hurricanes can threaten entire ecosystems by temporarily raising the sea level, eroding large parts of the fragile coastline, and contaminating delicate marshlands (PDF) with seawater.

Tornadoes' biggest threats to the environment stem from human activities. A twister could, conceivably, damage a waste storage or treatment facility, polluting surrounding areas. Or it could breach a chemical plant, unleashing toxic materials into the groundwater. While such incidents have almost certainly occurred on a small scale, the Lantern couldn't find any record of a tornado triggering a toxic release on a scale that would permanently endanger a local ecosystem.

Twisters have a documented history of spreading radioactive material. Dust devils—ground-level whirlwinds—have lofted radioactive materials from nuclear test sites half a mile into the air, enabling them to spread into surrounding areas. The worst-case scenario might involve one of the handful of nuclear reactors in Tornado Alley. An EF2 tornado—a lowish-strength tornado on the Enhanced Fujita scalestruck an Ohio nuclear reactor (PDF) in 1998. The storm knocked out power to the plant, forcing the facility to use backup power and channel it to the highest-priority systems. The temperature of the fuel storage pond rose from 110 degrees to 137 degrees in the course of one day. Power was restored before any serious environmental damage occurred, but it troubled many observers that a comparatively meek tornado could cause as much trouble as it did. It's possible, at least in theory, that a massive tornado carrying heavy projectiles could cause a catastrophic release of radioactivity.

The Lantern thanks John T. Snow of the University of Oklahoma.

Brian Palmer writes about science, medicine, and the environment for Slate and the Natural Resources Defense Council. Email him at explainerbrian@gmail.com. Follow him on Twitter.

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