  We use atomistic stochastic Landau-Lifshitz-Slonczewski simulations to study
the interaction between large thermal fluctuations and spin transfer torques in
the magnetic layers of spin valves. At temperatures near the Curie temperature
$T_{\rm C}$, spin currents measurably change the size of the magnetization
(i.e. there is a {\it longitudinal} spin transfer effect). The change in
magnetization of the free magnetic layer in a spin valve modifies the
temperature dependence of the applied field-applied current phase diagram for
temperatures near $T_{\rm C}$. These atomistic simulations can be accurately
described by a Landau-Lifshitz-Bloch + Slonczewski equation, which is a
thermally averaged mean field theory. Both the simulation and the mean field
theory show that a longitudinal spin transfer effect can be a substantial
fraction of the magnetization close to $T_{\rm C}$.
