T his paper describes a decision tree analysis to assess the cost-effectiveness of MANPADS (Man-Portable Air Defense Systems) countermeasures. These countermeasures are electronic devices that can be installed on commercial airplanes to detect and deflect surface-to-air missiles (SAMs) fired by terrorists. The model considers a terrorist attempt to shoot down a commercial airplane with a heat-seeking SAM, and it evaluates the decision to install countermeasures, taking into account alternative modes of attack, probabilities of success, and consequences to the economy. All model variables were fully parameterized, using reasonable ranges based on open-source literature. Not surprisingly, the probability of an attack, the consequences of an attack to the economy, and the cost of countermeasures are the most important parameters. Surprisingly, some of the hotly disputed parameters, such as the probability of an airplane surviving a successful hit or the probability of a false alarm, have very little impact on the results. The analysis suggests that MANPADS countermeasures installed on planes can be cost-effective if the probability of such an attack is large (greater than about 0.40 in ten years), the economic losses are large (greater than about $75 billion), and the countermeasures are relatively inexpensive (smaller than about $15 billion). An economic analysis conducted as part of this analysis showed that the economic impacts can be as large as $250 billion, thus making countermeasures a possibly cost-effective option. More research is needed to determine the real costs of MANPADS countermeasures and how terrorists may shift their tactics, once countermeasures are installed.

There are several important linkages among environmental hazards and crises caused (at least in part) by human‐caused global warming, and both homeland security and national security risk analysis and practice. Increasingly robust research has demonstrated (1) anthropogenic climate change and its interaction with other human environmental pressures (population, pollution, and resource consumption growth); (2) worsening climate disruption patterns and disaster projections, showing long‐range risk to the very survival of human civilization; and (3) links among environmental hazards, human economic and political instability, and development of political violence. This paper discusses how and why environmental security (ES) and homeland security (HS) are linked, including the threat‐multiplying aspect of climate disruption risk factors; briefly contextualizes their growing interconnectedness in both theory and policy practice; and reviews some of what is most recently known about the science of climate disruption. It reviews disaster mitigation and resilient adaptation policy implications of climate variables such as extreme heat and drought, extreme storms, sea level rise, ocean ecosystem damage, and food and water crises. Most U.S. government security‐related organizations now incorporate HS‐ES mission statements, but current environmental security risk management and planning investment is insufficient, and burdened by political obstruction and costly scientific uncertainties.

The worsening effects of human-caused climate change, as well as issues most American view as “homeland security” (HS) can be seen in the news almost every day. Yet most in the general public and even many in security-related fields do not connect the two arenas, even though climate change, and interrelated resource competition and conflicts that together make up the growing field of environmental security (ES), are increasingly important risk and response variables for homeland security and emergency management. Current climate change effects are already destructive and volatile, but the future projected impacts are likely to be severe and costly to the economic, political, and social health of many nations as well as to a large proportion of the world’s population. The focus of this paper is to describe and connect the evolving concepts of environmental security, homeland security, and national security (NS). Definitions and missions for each concept are discussed, consistent with current, even if contested, practice and theory. Better comparative analysis of these unique but intimately connected realms will help advance the development of more comprehensive and sustainable security policy and strategy.

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