  In this article, we extend our previous study of the $\pi$-$\pi$ scattering
lengths under the presence of an external magnetic field, including finite
temperature effects. The novelty of this work is precisely the introduction of
temperature into the discussion, and its interplay with the magnetic field. As
in the previous article, we base our analysis in the linear sigma-model, and
our calculations are exact within this context. Although the effects are
comparatively small, it is interesting to remark that magnetic field and
temperature display opposite effects over the scattering lengths.
