Hurricane Irma is currently tearing through the Caribbean, with its sights set on Florida, causing catastrophic damage and loss of life. Numerous news reports have attempted to capture the magnitude of Irma’s power. One particularly potent comparison, used in many places, relates Irma to all the bombs dropped during World War 2 (here, here ,here)
Of those three, only the Express gets the units right, since a Watt is a Joule per second, so talking about a Watt as an amount of energy doesn’t really make sense. By comparison, total global energy consumption in 2014 was 109,613 TWh, which equates to a power of 12.5 TW on average. So even if the units aren’t quite reported correctly, this storm is certainly very big.
The source of the number is MIT Professor of Atmospheric Science Kerry Emanuel. None of the articles describe how this estimate is arrived at, but a little googling reveals a great discussion of estimating a hurricanes power by the NOAA. This page quotes a 1999 paper by Emanuel himself, entitled ‘The power of a hurricane: An example of reckless driving on the information superhighway’. In the article, Emanuel estimates that hurricanes have power ratings of between 3TW and 30TW, placing Irma towards the lower end of these estimates, which does’t quite make sense to me – if anyone has thoughts on this, please leave something in the comments. In Emanuel’s estimate, the power of the hurricane scales with the cube of the wind velocity and the square of the radius.
Of some amount of irony is the article’s discussion of the unreliability of relating hurricane power to things like bombs. It concludes:
Estimating a hurricane’s power is clearly not an easy task – and making sure these estimates are accurately reported on the web even harder – even when an author has warned of these difficulties in the past.
Refs: Emanuel, K. A., (1999): “The power of a hurricane: An example of reckless driving on the information superhighway” Weather, 54, 107-108