A man holds a baby as migrants and refugees from Iran sit on railway tracks while waiting to cross the Greek-Macedonian border near Gevgelija, on November 24, 2015. [Photo/CFP]

Almost all those arriving came across the Mediterranean or the Aegean Seas, and half were Syrians fleeing the war. Another 20 percent were Afghans, and 7 percent were Iraqis, IOM and the UN refugee agency UNHCR said in a joint statement.

People smuggling operations probably accounted for the majority of journeys and likely earned at least $1 billion, Swing said, taking "anywhere from $2,000 to maybe $6,000 depending on how many members of the family and depending on which smuggling ring it is".