Introduction
[2] The concept of climate change Hot-Spot can be approached from the viewpoint of vulnerability or from that of climate response. In the former case a Hot-Spot can be defined as a region for which potential climate change impacts on the environment or different activity sectors can be particularly pronounced. In the latter case, a Hot-Spot can be defined as a region whose climate is especially responsive to global change. In particular, the characterization of climate response-based Hot-Spots can provide key information to identify and investigate primary processes of regional climate change. From these premises, here the response approach is adopted to investigate climate change Hot-Spots based on results from a multi-model ensemble of climate change simulations performed by modeling groups from around the world as contributions to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) (see the Program for Climate Model Diagnosis and Intercomparison, or PCMDI, http://www-pcmdi.llnl.gov).