In the wake of a magnitude 9.0 earthquake and the powerful tsunami that followed, the stricken nuclear reactors at Japan's Fukushima Daiichi power plant released not one but two powerful and invisible forces: radiation and fear of radiation.
Both can spread quickly, and with insidious stealth. They permeate walls, make no distinction between rich and poor, and are particularly hard on children.
And elevated levels of either can have long-term health consequences.
To be sure, to those living close to the Fukushima power plant or who have been told to avoid contaminated water, milk and spinach, the health threat posed by radiation is very real. And the ultimate scope of the accident is still unclear.
But as events continued to unfold last week, psychologists and engineers alike noted that fear of radiation had spread farther and more virulently than has radiation itself. And it may be just as dangerous.
"Radiation ticks all the boxes of things that make us frightened," says Jim Smith, a research professor in environmental physics at the University of Portsmouth in England. "It's invisible, we don't understand it, the images of Hiroshima and Nagasaki come to mind, and it causes cancer."
Fear of radiation can create stress, a potent physical and health risk all by itself, says risk perception expert David Ropeik, author of the 2010 book "How Risky Is It, Really? Why Our Fears Don't Always Match the Facts." It also can prompt people to make dangerous choices, including taking iodine pills that, for U.S. residents at least, were unnecessary and could have caused harm.
And, Ropeik says, fear of radiation can lead to policies "that can feel right but that are more dangerous," such as sticking with fossil fuels, which arguably carry greater risks to human health than does nuclear power. They're just risks we've learned to live with.
Using data from the U.S. Environmental Protection Agency, Ropeik calculates that 3,000 to 4,000 Americans die prematurely every year because they are exposed to fine particles in air pollution that are the direct result of burning coal and oil to generate electricity.
Compare that with the two explosions that destroyed the Chernobyl nuclear power station in 1986. Three workers were killed immediately, and 28 others died shortly thereafter due to acute radiation poisoning, according to the World Nuclear Assn., which supports the nuclear energy industry. Although cases of thyroid cancer soared 16-fold among the highly exposed population of children who drank radioactive milk, by 2005, the United Nations Scientific Committee on Effects of Atomic Radiation reported that only 15 had died. And the expected spate of solid tumors and leukemia among those in the path of Chernobyl's plume has fallen far short of projections.
While epidemiological data from Chernobyl has ranged widely, none has put the expected death toll higher than 8,000. That would be the equivalent of about two years' worth of U.S. deaths from the burning of fossil fuels for energy sources.
Here's another way to look at it: In a 2007 analysis published by the journal BMC Public Health, Smith tallied the premature deaths from air pollution, obesity, smoking and secondhand smoke and compared them to those attributable to radiation exposure from Chernobyl. He found that even for survivors who absorbed the most radiation, the average loss of life expectancy was "significantly lower than that caused by severe obesity or active smoking."
"All energy forms have tradeoffs," Ropeik says. "Some scare us more, so we avoid those. And we suffer the consequences of preferring other forms of energy that do more health damage but that don't scare us as much."
The crisis in Fukushima appears to have skewed those views even further. In a poll conducted from March 17 through March 20, public support for expanded nuclear power generation had tumbled to 39%, with 52% of Americans pronouncing themselves opposed, according to the Pew Research Center for the People and the Press. Only a year ago, support for nuclear power stood at an all-time high of 52%, with 41% opposed.
At the same time, 57% said they favored more offshore drilling for oil and gas — less than a year after the Deepwater Horizon rig exploded, killing 11 workers and spilling 206 million gallons of crude oil into the Gulf of Mexico. Although its total health effects have yet to be tallied, just 37% of Americans opposed a hike in oil and gas drilling.
Why does "radiophobia" have such a hold on us? Psychologists and specialists in risk analysis say several factors are at work.
Evolution has primed us well to recoil from things that signal a sudden increase in risk to life and limb. Instinctively, we react to snakes, thunder, the dark, the smell of rotting flesh or the sight of wildfire with fear or revulsion.
In the roughly 400 years that most humans have lived with growing technological complexity, the human brain has evolved little. The sights, sounds and smells of the risks we have created ourselves — hulking industrial power plants, towering cityscapes and supersonic jet aircraft — do not set off visceral alarm bells.
Instead of triggering "fight or flight" orders in the brain's most primitive regions, these complex and manmade risks are processed in parts of the brain responsible for higher reasoning.
But that doesn't make those choices rational, Ropeik says. "Perfectly fact-based rationality is an ideal, but it's also a myth," he says.
Every day, we make decisions about risk — whether to drive to work or ride a bike, for instance, or whether to buy organic or conventionally raised produce. We're rarely aware of the mental shortcuts we use in making those decisions, but cognitive psychologists say they're both powerful and predictable.
Paul Slovic, the University of Oregon psychologist who pioneered the study of risk psychology, calls this process "The Feeling of Risk," which is also the title of his 2010 book. It is the gut reaction to a potential source of danger that predisposes us to accept or reject it.
For starters, humans tend to downplay the dangers of the devil they have already learned to live with —burning fossil fuels to generate electricity — and to distort those that are unfamiliar, such as nuclear power.
Our perceptions of personal control over the risks we face make a difference too. Humans tend to feel more comfortable with radiation to which we expose ourselves voluntarily. The same person who would calmly accept her radiation exposure from a series of X-rays or a cross-country flight might fret for days over slightly elevated radiation levels from the Fukushima plant, even though they are much less dangerous, Ropeik says.
Finally, cognitive scientists know that we are far more scared of catastrophic risks that affect a lot of people in one place all at once than we are of risks that take their toll in slow motion, spread broadly across the human landscape. The deaths of 34,000 people in motor vehicle accidents last year does not rivet our attention. But a plane crash that claims the lives of 228 passengers at a time — such as the 2009 disappearance of an Air France jet over the Atlantic Ocean while en route from Rio de Janeiro to Paris — induces horror.
This stems from an impulse that evolutionary psychologists recognize as key to our survival as a species.
"Instinctively, we are more afraid of something that threatens to wipe out our species all at once," Ropeik says.