The sea ice in question is frozen ocean water that melts each summer and then refreezes each winter. It typically reaches its smallest "extent" in September and largest "extent" in March of each year.

The melting sea ice will have an indirect affect on raising global sea levels, says climatologist Claire Parkinson of NASA. Since Arctic sea ice is already floating in the ocean, its melting and refreezing cycles don't directly affect global sea levels.

However, the lack of Arctic sea ice allows the atmosphere to warm faster, causing land ice to melt — which can raise sea levels, Parkinson says.

This record loss of Arctic sea ice will have major effects on wildlife in the region from shrimp to walruses and polar bears, says Lou Leonard of the World Wildlife Fund, an environmental advocacy group.

 Sea-ice loss is forcing polar bears to swim longer distances to find stable ice or reach land, and walruses are losing their habitat — threatening the populations of both species, according to the wildlife fund.

If the lack of Arctic sea ice continues, one long-term benefit, though, could be to shipping, where summers free of ice will allow ships to traverse previously impassable routes. It will also allow for better exploration of mineral and oil reserves.

The ice typically doesn't reach its smallest point until September, so more melting is likely in the weeks ahead.

The data center, in Boulder, Colo., reported Monday that the extent of Arctic sea ice shrank to 1.58 million square miles on Sunday. That breaks the old record of 1.61 million square miles from 2007. Figures are based on satellite records dating back to 1979.

The ice has been melting unusually rapidly this summer: On average, 38,000 square miles of ice has been melting per day since June, an area about the size of Indiana each day.

"This is roughly twice as much as normal for this time of year," says scientist Walt Meier of the data center.

Once it's done melting, the ice could shrink to under 1.5 million square miles sometime in September, the data center says.

Summer sea ice is melting at a rate faster than was predicted by the Intergovernmental Panel on Climate Change, a United Nations group of several thousand scientists that issues reports on global warming every few years. The most recent report was in 2007, which predicted that the Arctic summer would be ice-free by 2100.

But as global temperatures continue to increase, Meier says "it's quite likely that the Arctic will be largely ice-free in the summer in 20 or 30 years."

While Arctic sea ice extent varies from year to year because of changeable weather conditions, ice extent has shown a dramatic overall decline over the past 30 years.

The pronounced decline in summer Arctic sea ice over the last decade is considered a strong signal of long-term climate change: Data center scientist Ted Scambos says the melt can be blamed mostly on global warming from man-made emissions of greenhouse gases.

While a large Arctic storm in early August appears to have helped to break up some of the 2012 sea ice and helped it to melt more quickly, the decline seen in in recent years is well outside the range of natural climate variability, says Meier.

However, other scientists report that global warming doesn't fully explain what's been going on in the Arctic. A recent study in the Proceedings of the National Academy of Sciences, led by John Michael Wallace of the University of Washington, found that most of the recent reduction in sea ice is due to natural variability.