A wide variety of regional assessments of the water‐related impacts of climatic change have been done over the past two decades, using different methods, approaches, climate models, and assumptions. As part of the Water Sector research for the National Assessment of the Implications of Climatic Variability and Change for the United States, several major summaries have been prepared, looking at the differences and similarities in results among regional research projects. Two such summaries are presented here, for the Colorado River Basin and the Sacramento River Basin. Both of these watersheds are vitally important to the social, economic, and ecological character of their regions; both are large snowmelt‐driven basins; both have extensive and complex water management systems in place; and both have had numerous, independent studies done on them. This review analyzes the models, methods, climate assumptions, and conclusions from these studies, and places them in the context of the new climate scenarios developed for the National Assessment. Some significant and consistent impacts have been identified for these basins, across a wide range of potential climate changes. Among the most important is the shift in the timing of runoff that results from changes in snowfall and snowmelt dynamics. This shift has been seen in every regional result across these two basins despite differences in models and climate change assumptions. The implications of these impacts for water management, planning, and policy are discussed.

An examination of the metadata for almost 900 bibliographic references on the effects of climate change and variability on U.S. water resources reveals strengths and weaknesses in our current knowledge. Considerable progress has been made in the modeling of climate change effects on first‐order systems such as regional hydrology, but significant work remains to be done in understanding subsequent effects on the second‐, third‐, and fourth‐order economic and social systems (e.g., agriculture, trade balance, and national economic development) that water affects. In order to remedy a recently‐revealed lack of understanding about climate change on the part of the public, climate and water scientists should collaborate with social scientists in illuminating the effects of climate change and variability on the systems that affect how and where most people live.

Terrorism is a constant and fearful phenomenon, as America has learned to its recent and terrible cost, and like the nine-headed hydra of ancient mythology, as soon as one group or method is terminated, more spring up to take its place. Environmental terrorism adds a new dimension to this phenomenon, identifying the target as a natural resource or environmental feature. At a time when populations all over the world are increasing, the existing resource base is being stretched to provide for more people, and is being consumed at a faster rate. As the value and vulnerability ofthese resources increases, so does their attractive ness as terrorist targets. History shows that access to resources has been a proximate cause of conflict, resources have been both tools and targets of conflict, and environmental degradation and disparity in the distribution of resources can cause major political controversy, tension, and violence. The purposeful destruction of a natural resource can now cause more deaths, property damage, political chaos, and other adverse effects than it would have in any previous decade. The choice of environmental resources as targets or tools ofterrorism is consistent with both the increasing lethality ofterrorism and the growing envi ronmental awareness on the part of the public. Copyright (c) 2002 Massachusetts Institute of Technology.

The term environment is often used as a short form for the biophysical environment, which refers to the biotic and abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. All life that has survived must have adapted to conditions of its environment. On one hand, part of the study of environmental science is the investigation of the effect of human activity on the environment. On the other hand, scholars also examine threats posed by environmental events and trends to individuals, communities, or nations, otherwise known as environmental security. It studies the impact of human conflict and international relations on the environment, or on how environmental problems cross state borders. Environmental security is a significant concept in two fields: international relations and international development. Within international development, projects may aim to improve aspects of environmental security such as food security or water security, along with connected aspects such as energy security. The importance of environmental security lies in the fact that it affects humankind and its institutions anywhere and at anytime. To the extent that humankind neglects to maintain the planet’s life-supporting eco-systems generating water, food, medicine, and clean air, current and future generations will be confronted with increasingly severe instances of environmentally induced changes.

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