This year, both the North-west and North-east passages were mostly ice free, as they have been twice since 2008.
Last month, the 74,000-tonne STI Heritage tanker passed through the North-east Passage with the assistance of ice breakers in just eight days on its way from Houston, Texas, to Thailand.
The north-east sea route, which links the Atlantic to the Pacific, is likely to become a commercial ship operator's favourite, saving thousands of miles and avoiding tolls on the Suez Canal tolls.
Further evidence of dramatic change in the Arctic came last week from Alan Hubbard, a Welsh glaciologist at Aberystwyth University, who has been studying the Petermann glacier in northern Greenland for several years.
The glacier, which covers about 6% of the icecap, is 186 miles (300km) long and up to 3,280ft (1km) high. In August last year, a 100 square-mile (260 sq km) block of ice calved from the glacier. Photographs show that by July this year it had melted and disappeared.
"I was gobsmacked. It [was] like looking into the Grand Canyon full of ice and coming back two years later to find it full of water," said Hubbard.
Last year (2010) tied with 2005 as the warmest year on record.
