Hurricane Katrina remains one of the worst natural disasters to occur on U.S. soil. It’s estimated that at least 1,833 people were killed in the hurricane and subsequent floods, and property damage was in the region of $81 billion. Conspiracy theories about Katrina flourished almost immediately, and remain prevalent to this day. Some theories merely allege that the levees were deliberately destroyed in an act of profiteering or ethnic cleansing; others claim that the hurricane was conjured up by the Bush government using secret military weather manipulation technology.

Now Hurricane Sandy is set to pass directly through New York City and continue north towards Canada. Because of its record-breaking size, much of the north-eastern United States, from the East Coast to the Great Lakes, will be affected. Extensive damage is being predicted. It should come as no surprise that some familiar old conspiracy theories are being dusted off and updated for 2012. Could Obama be using weather modification technology to turn the upcoming election in his favour? Professional conspiracy theorist Alex Jones is calling Sandy the ‘engineered storm of the century‘.

Will these theories remain popular after Hurricane Sandy has passed, like the Katrina theories have? I suspect it depends on how severe the consequences of Sandy are. Just over a year ago, Hurricane Irene threatened to do vast amounts of damage to New York City; the media were predicting major devastation and long-lasting consequences for the entire U.S. economy. In the days before Irene hit, the same kind of conspiracy theories were being passed around internet forums. Fortunately, Irene weakened and ultimately passed through New York without causing the chaos that had been predicted. The conspiracy theories fizzled out too.

Why have Hurricane Katrina conspiracy theories endured so much better than Hurricane Irene theories? It may have something to do with the proportionality bias. Patrick Leman referred to this psychological phenomenon as the ‘major event-major cause’ heuristic. We are unconsciously biased towards seeking proportionally grand, intricate, complex, and significant causes for grand, intricate, complex, or significant events. Explanations which meet this rule-of-thumb may seem more plausible and appealing than explanations which defy the intuitive logic of the proportionality bias. In his research, Leman found that conspiracist explanations were more likely to be endorsed for the successful assassination of a President than an assassination attempt which failed. In the real world, conspiracy theories of J.F.K.’s assassination have become mainstream while conspiracy theories about the unsuccessful attempt on Reagan’s life are few and far between. It’s easy to believe a lone, unknown, and possibly unbalanced individual can wound the most powerful person on the planet. But such an insignificant cause may seem insufficient when it comes to killing the most important person on the planet; a long-running, systematic, and nefarious conspiracy can begin to seem more plausible. The death of Princess Diana, the 9/11 attacks, Hurricane Katrina: these momentous and shocking events have all produced enduring conspiracy theories, while the Reagans and Irenes have been forgotten.

In reality, small causes sometimes have large effects. In the world of conspiracy theories, large effects demand a conspiracy. If Hurricane Sandy has the devastating effects that some are predicting, it’s entirely possible that conspiracy theories will flourish. If the devastation fails to materialise, the conspiracy theories will be forgotten. Personally I’m hoping for the latter.