Arctic sea ice has melted to the fourth lowest levels on record, reinforcing the long-term downward trend in ice cover in the polar region, scientists said.

The extent of the ice at the end of the annual summer melt shrank to close to low levels seen in 2007 and 2011, but melting was not as extreme as in current record year 2012, preliminary findings from the US National Snow and Ice Data Centre (NSIDC) showed.

Sea ice extent dropped to its lowest extent for the year of 4.41 million square kilometres, the fourth lowest minimum in satellite records and well below the average minimum for 1981 to 2010, the NSIDC data revealed.

The nine lowest levels of cover at the end of the summer melt recorded by satellites have all occurred in the last nine years.

Increasing melting in the Arctic is making the region more accessible to ships, fishing and oil exploration, and the scientists said both the Northern Sea Route, along the coast of Russia, and Roald Amundsen’s route through the Northwest Passage are open.

At the other end of the world, the maximum extent of the Antarctic ice cover following freezing over the winter is at average levels, in contrast with recent years when Antarctic winter extents reached record high levels.

Commenting on the findings, Colin Summerhayes, emeritus associate at the Scott Polar Research Institute, said: “The latest Arctic data from the NSIDC confirm that 2015 has the fourth lowest area amount of sea ice.

“It neatly shows that the downward trend in sea ice coverage is continuing, and not reversing as some supposed from the slight increases after 2012.

“There will always be some years when the amount of sea ice is above the downward trend line and some years when it is below the line. But regardless of these wiggles the trend line continues to fall, as forecast. That’s the big picture.”