In the preface to this book Nicholas Stern emphasizes the need for making climate change a priority. Postponing action against climate change, even for a few more years, increases the likelihood that we will be unable to hold GHG concentrations within the limits of acceptable risk, and makes mitigation more expensive in the future. This is largely due to the historical build-up of carbonintensive energy infrastructure that, along with the long economic lifetime of investments, results in a lock-in to a global high-emission development trajectory. Even if we manage to limit the global temperature rise to 2°C, the socioeconomic impacts could be devastating: water stress for billions of people, mass loss of species and flooding of populous coastal cities.