Backward Ricci Flow on Locally Homogeneous Three-manifolds
  In this paper, we study the backward Ricci flow on locally homogeneous 3-manifolds. We describe the long time behavior and show that, typically and after a proper re-scaling, there is convergence to a sub-Riemannian geometry. A similar behavior was observed by the authors in the case of the cross curvature flow. 
Xiaodong Cao, Laurent Saloff-Coste