A nuclear close call is an incident that might have led to at least one unintended nuclear detonation or explosion, but did not. These incidents typically involve a perceived imminent threat to a nuclear-armed country which could lead to retaliatory strikes against the perceived aggressor. The damage caused by international nuclear exchange is not necessarily limited to the participating countries, as the hypothesized rapid climate change associated with even small-scale regional nuclear war could threaten food production worldwide—a scenario known as nuclear famine. Despite a reduction in global nuclear tensions and major nuclear arms reductions after the end of the Cold War (in 1992), estimated nuclear warhead stockpiles total roughly 15,000 worldwide, with the United States and Russia holding 90% of the total. Though exact details on many nuclear close calls are hard to come by, the analysis of particular cases has highlighted the importance of a variety of factors in preventing accidents. At an international level, this includes the importance of context and outside mediation; at the national level, effectiveness in government communications, and involvement of key decision-makers; and, at the individual level, the decisive role of individuals in following intuition and prudent decision-making, often in violation of protocol. 1950s 5 November 1956 During the Suez Crisis, the North American Aerospace Defense Command (NORAD) received a number of simultaneous reports, including unidentified aircraft over Turkey, Soviet MiG-15 fighters over Syria, a downed British Canberra medium bomber, and unexpected maneuvers by the Soviet Black Sea Fleet through the Dardanelles that appeared to signal a Soviet offensive. Considering previous Soviet threats to use conventional missiles against France and the United Kingdom, U.S. forces believed these events could trigger a NATO nuclear strike against the Soviet Union. In fact, all reports of Soviet action turned out to be erroneous, misinterpreted, or exaggerated. The perceived threat was due to a coincidental combination of events, including a wedge of swans over Turkey, a fighter escort for Syrian President Shukri al-Quwatli returning from Moscow, a British bomber brought down by mechanical issues, and scheduled exercises of the Soviet fleet. Late 1958 U.S. Secretary of State Christian Herter characterized the Second Taiwan Strait Crisis as "the first serious nuclear crisis". In this conflict, the PRC shelled the islands of Kinmen (Quemoy) and the Matsu Islands along the east coast of mainland China (in the Taiwan Strait) to "liberate" Taiwan from the Chinese Nationalist Party, also known