  Non-linear CMB temperature anisotropies up to the third-order on large scales
are calculated. On large scales and in the Sachs-Wolfe limit, we give the
explicit expression for the observed temperature anisotropy in terms of the
primordial curvature perturbation up to the third-order. We derived the final
bispectrum and trispectrum of anisotropies and the corresponding non-linear
parameters, in which the contributions to the observed non-Gaussianity from
primordial perturbations and from the non-linear mapping from primordial
curvature perturbation to the temperature anisotropy are transparently
separated.
