Five ways for humans to trigger a natural disaster

clouds by providing something for water to condense on. It is difficult, though, if not impossible, to establish how much rainfall is a direct result of cloud seeding. Don Griffith, of North American Weather Consultants, says it is highly unlikely that cloud seeding could trigger a flood on the scale of the one that devastated Rapid City in 1972. “In truth it was probably a bad idea for the scientists to be cloud seeding while a storm was building,” says Griffith. “But man’s ability to modify the weather in some small measure can in no way match power of nature.” Kerry Emanuel of Massachusetts Institute of Technology agrees that humans probably cannot influence such a large storm. “Cloud seeders often have the opposite problem: they don’t know whether they’ve had an effect at all,” he says.

* Hurricanes: Worryingly, hurricanes can also be seeded. In the 1960s U.S. scientists involved in a project called Stormfury sought to demonstrate that they could disrupt the structure and energy of a hurricane by seeding the atmosphere. After two decades, some scientists suggested that Stormfury had failed to induce any change and the project was cancelled. But hurricane expert Kerry Emanuel says controlling the path of a hurricane is something that “we know how to do theoretically.” Emanuel explains that two-thirds of the hurricanes on course to make landfall in the United States are knocked off course by another weather system. So scientists know what temperature and pressure disturbances in the atmosphere will help divert a raging hurricane. “The evolution of the atmosphere is very sensitive to small perturbations,” Emanuel adds.

One way to create the necessary disturbances would be to release a trail of black carbon — tiny soot particles — into the sky. This should absorb enough of the Sun’s energy to create a temperature disturbance. Rerouting a hurricane, however, would be an incredibly risky job that could result in international conflict and countless lawsuits. “If there is an 80% chance a storm is going to hit Miami, and if diverting it creates a 10% chance it will hit Bermuda - what do you do?” Emanuel wonders. Partly for these reasons, government agencies have so far steered clear of steering hurricanes. However, the prospect could become too appealing not to test. “For now, it is just an idea. But if we get a few more Katrinas and it becomes widely known that scientists have a technique to shift hurricane paths, it could become less taboo,” says Emanuel. “In my view it is inevitable that it will be tried, but that may not be in our lifetime.”