Environmental security focuses on the ecological conditions necessary for sustainable development. It encompasses discussions of the relationships between environmental change and conflict as well as the larger global policy issues linking resources and international relations to the necessity for doing both development and security differently. Climate change has become an increasingly important part of the discussion as its consequences have become increasingly clear. What is not at all clear is in what circumstances climate change may turn out to be threat multiplier leading to conflict. Earth system science findings and the recognition of the scale of human transformations of nature in what is understood in the 21st century to be a new geological epoch, the Anthropocene, now require environmental security to be thought of in terms of preventing the worst dangers of fragile states being unable to cope with the stresses caused by rapid environmental change or perhaps the economic disruptions caused by necessary transitions to a post fossil fueled economic system. But so far, at least, this focus on avoiding the worst consequences of future climate change has not displaced traditional policies of energy security that primarily ensure supplies of fossil fuels to power economic growth. Failure to make this transition will lead to further rapid disruptions of climate and add impetus to proposals to artificially intervene in the earth system using geoengineering techniques, which might in turn generate further conflicts from states with different interests in how the earth system is shaped in future. While the Paris Agreement on Climate Change recognized the urgency of tackling climate change, the topic has not become security policy priority for most states, nor yet for the United Nations, despite numerous policy efforts to securitize climate change and instigate emergency responses to deal with the issue. More optimistic interpretations of the future suggest possibilities of using environmental actions to facilitate peace building and a more constructive approach to shaping earth’s future.