The environment is the planetary support system on which all other human enterprises depend. If political, social, cultural, religious, and most importantly economic systems are to remain secure and viable, the environment must also remain secure and viable. This makes global environmental conditions a legitimate U.S. national security concern. The security of individuals, communities, nations, and the entire global community is increasingly jeopardized by unpremeditated, non-military environmental threats. These threats are self-generated: we perpetrate them on ourselves, by fouling our air and water, and over-harvesting our land. These threats are not felt equally around the world. Southern countries face severe problems from desertification, while northern industrial countries deal with acid rain, and the polar regions see large depositions of persistent organic chemical pollutants. Climate change will cause uneven effects over the entire globe for the next fifty to 100 years, with some countries benefiting and others suffering. Ensuring environmental security means accepting a new definition of what it means to be secure: that a military response is not applicable to all security threats, and that we must consider trans-boundary, cooperative solutions.