The Arctic will be practically ice-free during the summer within three decades, according to the top U.S. ice observer. But, he is quick to add, with climate change, some good comes with the bad.

"I'm a climate scientist, but I'm also a realist on this," said Mark Serreze, director of the National Snow and Ice Data Center.

Each summer, arctic ice has been disappearing little by little. In July, it shrank to the least coverage that satellites have recorded for that month, measurements showed.

"This is just part and parcel of the decline that we've seen in the overall ice extent because the Arctic is warming up," Serreze said.

The center, which operates out of the University of Colorado at Boulder, with support of NASA, said the average ice extent was 3.06 million square miles, 81,000 square miles below the previous record low in 2007, and 842,000 square miles below average.

Satellite records date to 1979, but observations by ship and plane go back to the 1950s, Serreze said. July's ice coverage "is certainly the lowest in, oh, the last 50 or 60 years that we have reliable records for," he said.

The data center scientists also said that the oldest ice in the Arctic, which tends to be the thickest and most resistant to melting, is declining.

"The Arctic is the heat sink of the Northern Hemisphere," Serreze said. "The ice cover is highly reflective. If you lose that ice cover, you change the heat budget of the Arctic."

Overall climates, and weather patterns below the Arctic, are likely to be affected by this changed budget, he said.

"This is man-made; there seems to be little doubt in that," Serreze said. "It would be reversible if we were to do something about our carbon dioxide emissions, but I don't see much of a fat chance in hell we're going to see any change here. We're going to have to adapt."

And those changes in climates, he said, will have a serious impact on rising sea levels, loss of habitat for Arctic fauna, drinking water shortages, territorial disputes over newly open waters and more.

But good comes with the bad, Serreze said: warmer winters, springs will extend growing seasons, and even allow farming to happen in place where it hadn't before.

Another benefit? Increased navigation.

According to the data center, a tanker set sail from Murmansk, Russia, on June 29 and completed a crossing of the Kara and Barents seas on July 14. The same company plans to send at least six or seven more ships along the same route this summer.

"We will adapt, because we have to," Serreze said.