On December 5, 1952, the Great Smog of London enveloped the city in a thick, deadly fog, caused by a combination of coal smoke and weather conditions. The smog lasted for several days, and it is estimated that up to 12,000 people died as a result of respiratory issues caused by the pollution. The disaster exposed the severe health risks of air pollution and led to significant changes in environmental policies in the UK. It prompted the British government to pass the Clean Air Act of 1956. The event also raised global awareness of the need for pollution control.