A forest fire has no "typical" size: a small grass burn and a firestorm covering thousands of hectares are part of the same phenomenon. The same goes for tropical cyclones: the energy they release over their lifetime does not cluster around some average value. Instead, it follows a power law, and this rule holds across all of Earth's oceans.
Scientists calculated the power dissipation index for 469 cyclones in the North Atlantic and for hundreds more in the other three basins. This index sums the cube of wind speed every six hours of a storm's life, measuring how much energy the cyclone spent on friction against water and land. The shape of the distribution has not changed for decades: the active decade of 1995–2005 is indistinguishable from 1926–1970.
Warm years and El Niño shift the upper bound of the distribution, allowing more powerful hurricanes to emerge. But the curve itself remains the same, as if climate merely stretches the ruler without changing its markings. This suggests that the atmosphere sits near a critical state, where any gust can cascade into a storm.
This view links tropical cyclones to earthquakes and forest fires, which also follow power laws. For climate science, it means we can assess the risk of extreme hurricanes even without knowing exactly when the next one will strike.
An exponent near 1 means that energy is distributed such that each order of magnitude in PDI contains roughly the same number of cyclones. This property is typical of earthquakes and forest fires.