PARIS &#8212 Arctic ice has shrunk to the lowest level on record, satellite images show, raising the possibility that the Northwest Passage that eluded famous explorers will become an open shipping lane.

The European Space Agency said nearly 200 satellite photos showed an ice-free passage along northern Canada, Alaska and Greenland, and ice retreating to its lowest level since such images were first taken in 1978.

The waters are exposing unexplored resources. Seasonal changes in ice levels already opened a slim summer window for ships.

Leif Toudal Pedersen, of the Danish National Space Center, said that Arctic ice has shrunk to some 1 million square miles. The previous low was 1.5 million square miles, in 2005.