Competition over resources
In the environmentally constrained but more populous world that can be expected over the course of this century, there will be greater scarcity of three key resources: food, water and energy. Demand for all three resources is already beyond that which can be sustained at current levels. Once population growth and the effects of climate change are factored in, it is clear that greater competition for such resources should be expected, both within and between countries, potentially leading in extreme cases to conflict.
This major report was the result of an 18-month long research project examining the various threats to global security, and sustainable responses to those threats. 
Many leading military analysts in the United States are increasingly alert to the link between security and climate change. Is international terrorism really the single greatest threat to world security? 