  We study the chaotic nature of spin glasses against perturbations of the
realization of the quenched disorder. This type of perturbation modifies the
energy landscape of the system without adding extensive energy. We exactly
solve the mean-field case, which displays a very similar chaos to that observed
under magnetic field perturbations, and discuss the possible extension of these
results to the case of short-ranged models. It appears that dimension four
plays the role of a specific critical dimension where mean-field theory is
valid. We present numerical simulation results which support our main
conclusions.
