  We study local temperature fluctuations in a 2+1 dimensional CFT on the
sphere, dual to a black hole in asymptotically AdS spacetime. The fluctuation
spectrum is governed by the lowest-lying hydrodynamic modes of the system whose
frequency and damping rate determine whether temperature fluctuations are
thermal or quantum. We calculate numerically the corresponding quasinormal
frequencies and match the result with the hydrodynamics of the dual CFT at
large temperature. As a by-product of our analysis we determine the appropriate
boundary conditions for calculating low-lying quasinormal modes for a
four-dimensional Reissner-Nordstr\"om black hole in global AdS.
