  The influence of climate variability and global warming on the occurrence of
tropical cyclones (TC) is a controversial issue. Existing historical databases
on the subject are not fully reliable, but a more fundamental hindrance is the
lack of basic understanding regarding the intrinsic nature of tropical cyclone
genesis and evolution. It is known that tropical cyclones involve more than a
passive response to changing external forcing, but it is not clear which
dynamic behaviour best describes them. Here we present a new approach based on
the application of the power dissipation index (PDI), which constitutes an
estimation of released energy, to individual tropical cyclones. A robust law
emerges for the statistics of PDI, valid in four different ocean basins and
over long time periods. In addition to suggesting a novel description of the
physics of tropical cyclones in terms of critical phenomena, the law allows to
quantify their response to changing climatic conditions, with an increase in
the largest PDI values with sea surface temperature or the presence of El Nino
phenomenon, depending on the basin under consideration. In this way, we
demonstrate that the recent upswing in North Atlantic hurricane activity does
not involve TCs quantitatively different from those in other sustained
high-activity periods prior to 1970.
