Climate change poses a growing security threat and could cause conflict in the Arctic, a group of retired American generals and admirals said on Tuesday.

In a new report, the former military officers said the Pentagon had been caught out by the rapid changes under way in the Arctic because of the melting of the sea ice.

• Trip of a lifetime would take the best part of three weeks through picturesque Alaska and Siberia
• Russia set to complete extension of rail network to tip of Siberia by 2030
• $99 billion plan would see 65-mile tunnel bored under Bering Strait and linking East and West

The prospect of an epic train journey from New York to London might seem like a distant dream for those seeking the ultimate railway holiday.