Has melt reached tipping point where retreat cannot be halted?

Here's the good news: this summer's Arctic ice melt means an early start to the Hudson Bay shipping season.

Forecasts show Coast Guard icebreakers will no longer be necessary for shipping to Churchill after July 16.

That's 15 days earlier than the average ice-free shipping date of July 31, which means re-supply barges should able to reach communities in Nunavut's Kivalliq and Kitikmeot regions that much earlier.

But the down side to the retreat of the Arctic's thin ice cover is a 50-50 chance that the North Pole will become ice-free this September – for the first time in more than 100,000 years.

"The North Pole is where there's supposed to be ice," said environmental scientist Mark Serreze in a recent telephone interview from the U.S. National Snow and Ice Data Center in Colorado.

Scientists like Serreze say the weakness of the ice that's melting is responsible for the retreat of Arctic sea ice.

As old ice melts, a development linked to rising water and air temperatures, the new, thin ice that forms in its place in the winter tends to melt much more rapidly in the spring and summer.

During the month of April, scientists determined that the Arctic's increasingly flimsy sea ice cover shrank by 6,000 square kilometres every day.

If this ice continues to melt at the same rate as in 2007, scientists predict that only 2.22 million sq km of ice – less than the size of Nunavut – will remain in the Arctic Ocean this September. This would be much less than the record low of 4.28 million sq km set in 2007.

A major concern is whether the Arctic ice melt has reached a "tipping point," where even tough measures to curb global warming won't stop its final retreat.

After this tipping point is reached, the Arctic Ocean is expected to settle into an ice-free state every summer.

Tipping points were the hot topic at last week's Arctic Forum conference in Washington, D.C., where scientists looked at the potential consequences of these "points of no return" on the environment and people.

The impact of tipping points may explain why the Norse in Greenland died out during the 1400s.

The Norse settlers were unable to deal with several changes occurring at the same time, suggested researcher Tom McGovern in his talk, "Well adapted but still extinct: Norse Greenland in new perspective."

Today's sea ice loss is expected to deliver many environmental changes, which will compound other social, economic and political stresses in the circumpolar world.

New scientific information about Arctic sea ice loss played into last week's decision by the United States Fish and Wildlife Service to list polar bears as "threatened."

Scientists expect that as sea ice thins, melts and retreats, open water will allow even more heat to enter the Arctic Ocean. This warmer ocean will in turn heat the land and melt glaciers where they flow into the water.

As Greenland's ice sheet melts, sea levels may rise, threatening many coastal, low-lying communities.

The stream of icebergs, recently seen off Newfoundland and Labrador, originate from glaciers in Greenland. Scientists suspect these icebergs reflect the breakdown of the island's huge ice sheet, which is occurring many times faster than scientists believed possible.

Over the short term, an ice-free Arctic Ocean will open up new possibilities, including easier access to natural resources and new transportation routes.

The Northern sea route, the shipping lane from the Atlantic Ocean to the Pacific Ocean along the Siberian coast, is expected to open up this summer, and the Northwest Passage through Nunavut waters is also likely to be navigable by August.