Travellers to and around northern Europe have something to worry about. Smoke billowing out of Iceland's Bardarbunga volcano has forced the meteorological office to raise their risk level to the aviation industry for an eruption to orange, which is the third level on a four-grade scale. The colour codes, which are in accordance with recommended International Civil Aviation Organisation procedures, are intended to inform the aviation sector about a volcano's status. Code Red, that follows orange, is the highest.