  We study a two dimensional dilaton gravity system, recently examined by
Almheiri and Polchinski, which describes near extremal black holes, or more
generally, nearly $AdS_2$ spacetimes. The asymptotic symmetries of $AdS_2$ are
all the time reparametrizations of the boundary. These symmetries are
spontaneously broken by the $AdS_2$ geometry and they are explicitly broken by
the small deformation away from $AdS_2$. This pattern of spontaneous plus
explicit symmetry breaking governs the gravitational backreaction of the
system. It determines several gravitational properties such as the linear in
temperature dependence of the near extremal entropy as well as the
gravitational corrections to correlation functions. These corrections include
the ones determining the growth of out of time order correlators that is
indicative of chaos. These gravitational aspects can be described in terms of a
Schwarzian derivative effective action for a reparametrization.
