With the onset of industrialization, humans started to add significantly to the concentration of greenhouse gases in the atmosphere, in particular through carbon dioxide emissions as a consequence of fossil fuel burning. Anthropogenic climate change has emerged as one of the main problems of the 21st century. It is now a global political priority as it poses a real and potentially catastrophic threat to human and other life on this planet (IPCC 2007a; Oreskes 2005.) Without exaggeration, one can describe the situation as the most serious global environmental problem that humanity has ever faced (Gardiner 2011b, VII). Strategies to deal with climate change and its possible consequences are imbued with non-certainty, that is with risk, uncertainty and ignorance as defined below. This DK sets out to reach a better understanding of climate change noncertainties and, by doing so, to develop criteria for thresholds, defined as critical points, where different systems on different levels face important threats to their continual existence. These considerations will be connected with the development and evaluation of possible strategies to cope with climate change. Therefore, research projects undertaken within the proposed DK are meant to contribute to answering three questions: 1. How to understand and deal with climate change non-certainties in the natural and social sciences as well as from the perspective of normative theories? 2. What are the critical thresholds of environmental, social and economic systems considering their vulnerability and resilience and how are these thresholds related to the normative threshold of sufficiency, that is, the threshold of well-being below which persons’ basic rights are infringed or violated? 3. What are scientifically sound, technologically and institutionally feasible, economically efficient, and ethically defensible and sustainable strategies for responding to climate change, taking into account in particular the systematic problems of implementation in an environment characterized by non certainties and thresholds?