The portfolio of approaches to respond to the challenges posed by anthropogenic climate change has broadened beyond mitigation and adaptation with the recent discussion of potential climate engineering options. How to define and categorize climate engineering options has been a recurring issue in both public and specialist discussions. We assert here that current definitions of mitigation, adaptation, and climate engineering are ambiguous, overlap with each other and thus contribute to confusing the discourse on how to tackle anthropogenic climate change. We propose a new and more inclusive categorization into five different classes: anthropogenic emissions reductions (AER), territorial or domestic removal of atmospheric CO 2 and other greenhouse gases (D-GGR), trans-territorial removal of atmospheric CO 2 and other greenhouse gases (T-GGR), regional to planetary targeted climate modification (TCM), and climate change adaptation measures (including local targeted climate and environmental modification, abbreviated CCAM). Thus, we suggest that techniques for domestic greenhouse gas removal might better be thought of as forming a separate category alongside more traditional mitigation techniques that consist of emissions reductions. Local targeted climate modification can be seen as an adaptation measure as long as there are no detectable remote environmental effects. In both cases, the scale and intensity of action are essential attributes from the technological, climatic, and political viewpoints. While some of the boundaries in this revised classification depend on policy and judgement, it offers a foundation for debating on how to define and categorize climate engineering options and differentiate them from both mitigation and adaptation measures to climate change.

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Climate change may have dramatic consequences for several regions. Most vulnerable are fragile countries with limited capacities to adapt. Without timely action, the stresses induced by climate change may increase the risk of violent conflict. Designing and implementing adaptation strategies is becoming imperative to mitigate conflict potentials and prevent escalation. This article will discuss existing national and international approaches with focus on the UNFCCC process. It will be emphasized that a purely technical understanding of adaptation is insufficient to cope with the socio-political consequences of climate change. Indeed, adaptation may even contribute to conflict potentials if ill-designed. Thus, it is necessary to develop conflict-sensitive approaches complemented by internationally supported capacity development measures.

This article reviews the conflict potential of climate engineering (CE) against the background of possible security im plications of climate change. A conceptual framework is used to compare the technologies for carbon removal and solar radiation management regarding different characteristics and to assess the causes and drivers of potential conflict. Although CE measures may possibly reduce climaterelated conflicts, they could also intensify already existing international conflict structures or add new dimensions of conflict, in particular if their impacts are highly uncertain, quick, strong and heterogeneous, where the sever ity can vary regionally. While carbon engineering requires large resources and thus may contribute to resource conflicts, solar engineering is usually less costly and more efficient, but has numerous anticipated sideeffects that could cause novel conflicts and security implications in the international system. To avoid serious conflicts, regulative mechanisms and institutional structures are needed, building on the ENMODConvention that restrains military or hostile use of environmental modification. Given the high uncertainties, anticipative and adaptive governance structures that involve stakeholders and their perspectives are necessary.