Anthropogenic climate change is “one of the greatest challenges of our time” as affirmed by the governments of the world. The newest comprehensive assessment Climate Change 2013: The Physical Science Basis by the Intergovernmental Panel on Climate Change (IPCC) documents a rapidly and profoundly changing Earth System and provides the latest understanding of changes ahead of us. The most important findings, approved by the governments are: (i) Warming of the climate system is unequivocal; (ii) It is extremely likely that human influence is the dominant cause of the observed warming since the mid-20th century; and (iii) Limiting climate change will require substantial and sustained reductions in greenhouse gas emissions. These scientific findings, in combination with the declared ambition to limit global mean warming to 2°C, create an urgency for decisions and actions.