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It's not hard to imagine the damage weird weather inflicts on our planet. Hurricane Katrina, for example, obliterated coastal communities, wiped out businesses and left hundreds of dead bodies in its wake. Quantifying the dollar cost of such a one-off (we hope) event is pretty easy too: Katrina left us with a bill of $81 billion, according to the National Hurricane Center. But what about the year-in, year-out price tag of our increasingly volatile weather? It's a whole lot harder to calculate the cost of a chronic condition like that — or at least it was. Now, a study by the National Center for Atmospheric Research (NCAR) estimates that the bottom line cost of all the meteorological craziness is a staggering $485 billion per year in the U.S. alone, up to 3.4 percent of our country's GDP.

"It's clear that our economy isn't weatherproof," Jeffrey Lazo, the study's lead author, said in a statement. "Even routine changes in the weather can add up to substantial impacts on the U.S. economy."

The fact that it took until now for someone to try to come up with a hard figure like this is a measure of just how daunting the number-crunching can be. After all, when it comes to the weather yo-yo, a debit to one industry can be a credit to another. Take what happens in a snowstorm: air travel is disrupted and heating costs skyrocket, but ski resorts hit the jackpot. Or take a dry spell: crop supplies dwindle, but construction projects are able to stay on schedule.

Other industries are affected in myriad other ways. If you work in mining, you absolutely hate weird weather events, which eat up 14% of the mining economy each year, probably through several avenues: price fluctuations as demand for oil, gas, and coal changes in tandem with the weather; threats to the security of mine water supply; and damage to mines and associated transport infrastructure. Agriculture cuts a close second at 12%; no surprise, crops deal with torrential rain and unreliable temperatures even worse than we do. The manufacturing, finance, insurance, retail and utilities sectors are also particularly sensitive: people don't buy as many bikinis and bikes in rainy summers, and weather-induced power outages are a huge blow to electric utility operations. But be thankful if you are in wholesale trade, retail trade, or services. These are barely touched by the weather, partly because manufacturers cannot function without wholesalers no matter what the climate; and America still needs its health care and financial advice even when it's raining.

Lazo also found that different states have different vulnerabilities to wild weather. New York was the most sensitive, with weather having a 13.5% impact on its gross state product, and Tennessee fared best with only a 2.5% impact. While the researchers did not provide a concrete explanation for all of the state-to-state differences, they noted that states with a larger gross state product, or larger economic outputs, are more weather-sensitive in absolute terms. (A 10% loss of economic activity in a big-revenue state is simply a lot more money than the same 10% in a smaller state.) Differences may also arise from the fact that coastal regions are hit hardest by tropical storms, while other areas are more susceptible to drought and severe winters. But the study noted that no one part of the country seemed radically more weather sensitive than any other part.

No matter the regional differences, $485 billion is a lot of money, and it remains to be seen how effectively Americans will respond to the threat. If a recent survey by the HNTB Corporation, an infractructure contracting group, is any indication, we have a lot of work to do . Over two thirds of Americans don't realize that flooding is the biggest natural threat to their home, for example; fewer than 1 in 10 have prepared their homes for flooding, and 63% refuse to pay more taxes for flood-protective measures in their neighborhoods.

Floods are only one part of the weird weather picture, but HNTB flood management practice leader Rob Vining says the survey's findings are a perfect example of how we do a much better job of reacting to disasters than preparing for them. That may be human nature, but it's a part of our nature we have to learn to fight. If a broken planet isn't enough to mobilize us, a flat-broke country ought to be.

• Tara Thean