An emergency population warning is a method whereby local, regional, or national authorities can contact members of the public en masse to warn them of an impending emergency. These warnings may be necessary for a number of reasons, including: weather emergencies such as tornadoes, hurricanes, and ice storms; geological disasters such as earthquakes, landslides, volcanic eruptions, and tsunamis; industrial disasters such as the release of toxic gas or contamination of river water; radiological disasters such as a nuclear plant disaster; medical emergencies such as an outbreak of a fast-moving infectious disease; warfare or acts of terrorism. Many local areas use emergency population warnings to advise of prison escapes, abducted children, emergency telephone number outages, and other events. Requirements In order to develop an effective emergency warning system, certain things are required: an agreement as to what constitutes an emergency in the area served by the system. This differs from region to region depending on the local climate, geology, and the like. an agreement as to who can initiate an alert. In some countries all warnings are transmitted by a single command center, while in others (such as the United States) a host of local, regional, and national agencies are authorized to initiate warnings. a system or systems by which the information can be quickly transmitted to the population. an education program to teach the general public how to recognize an alert or what to do if a warning is broadcast. United Nations program Early warning system is the term that the International Early Warning Programme coordinated by the United Nations uses for all systems that are used to send emergency population warnings. The United Nations Development Programme uses the Send Word Now Emergency Notification System to alert its worldwide staff when an urgent situation arises. Methods by country Australia The Standard Emergency Warning Signal was originally adopted by the Bureau of Meteorology in the 1970s for tropical cyclone warnings. It became a standard national emergency warning signal in 1995. It can be broadcast on radio, television, automated telephone calls and in some places by public address systems in the event of bushfire, flood, cyclone, tsunami, earthquake or terrorist attack. If there is an emergency, Community Alert sirens will sound to alert the community to be impacted. There are Disaster Alert siren, Tornado Alert siren, Fire Tornado Alert siren, Tsunami Alert siren, Civic defence siren, Flood Alert siren, Hurricane Alert siren,