Canadian warships were sailing towards the Arctic yesterday in the latest act of gunboat diplomacy over control of the frozen wastes there. Ottawa has launched a series of Arctic sovereignty patrols to assert its territorial claims and fend off rivals, Denmark, Norway, Russia and the United States. Map of disputed area Its scramble for the Arctic is a consequence of global warming and the retreat of the polar ice. This has raised the prospect of once-inaccessible areas becoming available for oil and mineral extraction. It has also revived the dream of a "North-West Passage" for shipping, linking the Atlantic and...