  The Gaia hypothesis (Lovelock and Margulis, 1974) proposes that there is a
control system operating at global level that regulates climate and chemistry
at a habitable state for the biota. Here we provide statistically significant
observational evidence that a feedback control system moderating atmospheric
temperature is presently operating coherently at global scale, that is to say,
observational evidence for Gaia. Further, this control system is of a
sophisticated type, involving the corrective feedback not only of a linear
error term but also its derivative and its integral. This makes it of the same
type as the most commonly used control system developed by humans, the
proportional-integral-derivative (PID) control system.
