The first Homeland Security Secretary Tom Ridge unveils a color-coded terrorism warning system on March 12, 2002, in Washington, D.C.

AP Photo/Joe Marquette

Changing Terror Alert Levels

­In August of 2006, British authorities arrested several individuals who were linked to an alleged plot to destroy multiple commercial aircraft while en route from the United Kingdom to the United States. As a result of these events, both the U.S. and British governments elevated their terror warnings.

While law enforcement on both sides of the Atlantic were fairly certain that the threat had been significantly disrupted, there was still the possibility that they'd missed something. Somewhere out there, a terrorist operative might have fallen through the cracks of the investigation and might be making his or her way through the airport with liquid explosives disguised as a beverage or hair gel. The prevention of catastrophe might very well fall to tighter security measures or a civilian's heightened suspicion. Such a raised level of alertness might also deter terrorists from going through with an attempt.

This scenario illustrates a circumstance in which the U.S. Department of Homeland Security would change the national terror alert level. A possible threat existed, making it beneficial for security and law enforcement personnel to tighten preventative measures and for everyone else to remain a little more mindful of their surroundings. As you might imagine, the DHS depends on intelligence gathered by cooperating foreign governments, as well as the 15 other agencies that make up the U.S. intelligence community. The DHS also employs the Homeland Security Information Network, a computer-based communication system that allows state, local and federal agencies to collect and disseminate information related to terror prevention in real time.

In the United States, the attorney general consults with the DHS secretary, a presidential appointee, to assign threat conditions nationally, regionally, by sector (such as mass transit systems or bridges) or to a potential target (such as a sports stadium). In addition, alerts can be made by DHS personnel at the state and local levels.

DHS personnel make the decision based on available intelligence, terrorist capacity, terrorist intentions and timescale. In other words, intelligence is weighed against what terrorists are capable of, what terrorists want to do and how long they need to do it. The key determining factors for the usefulness of the intelligence, as listed by the DHS, are credibility of data, corroboration of data, timeliness of threat and the severity of threat. In the United Kingdom, the Joint Terrorism Analysis Centre determines threat level using a similar methodology.

While, in theory, determining a terror alert level is a matter of applying available intelligence to the security needs of certain areas, it's far from a perfect science. Many of the countries that employ terror alerts continue to fine-tune their system. For instance, while the post-Sept. 11 trend was to cast one, expansive net over existing alert systems, nations such as Australia have recently made efforts to allow threat levels to apply to specific locations and industries, as opposed to a national threat level.

In the United States, the DHS was heavily criticized during the 2004 presidential elections. Critics, such as political rivals Howard Dean and John Kerry charged that President George W. Bush used the terror alert system to boost his own re-election campaign and distract from domestic issues. The Bush administration vehemently denied these accusations, but they underlined a key flaw of the system: perceived ambiguity. Does the public understand why the nation is at a given threat level and, if not, how does this affect their response? If the DHS is merely crying wolf by maintaining threat level yellow, then what's the point?

Critics have called for better communication on the reasons for terror alert level changes, as well as the possible discontinuation of threat levels blue (guarded) and green (low), as they have never been issued. Some critics even go so far as to suggest that terror alerts could provide terrorists useful information in planning attacks.

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