The discovery of an empirical law that governs tropical cyclones is reported online in Nature Physics this week. The effect of climate change on tropical cyclones is highly controversial, because such storms are not fully understood; therefore this work has implications for the debate.

Prior to satellite imaging of storms, historical records were incomplete. Alvaro Corral and co-workers solve this problem by focusing on the total energy released by individual storms, for which the methods developed for the physics of critical behaviour are available. They find that although small storms greatly outnumber large storms, the relative proportion of small to large ones is the same across four different ocean basins over several decades in time. They also note that the maximum energy is set by the size of the basin.

What is affected by the rising sea surface temperature is the proportion of large cyclones. However, despite the increased hurricane activity in the North Atlantic during 1995-2005, individual hurricanes have not released more energy when compared to other active periods before 1970.