ABC News’ Clayton Sandell reports:

Did Arctic sea ice melt to a record low level this summer?

Researchers at the University of Bremen in Germany believe that it did, dipping 27,000 square kilometers below the previous record low set in 2007.

However, U.S. scientists at the National Snow and Ice Data Center in Boulder, Colo., are not ready to declare that the extent of Arctic sea ice has dropped below the record level.  At this point, the expectation is that 2011 will rank second — right behind 2007 — for record Arctic sea ice melt. Scientists at the International Arctic Research Center in cooperation with the Japan Aerospace Exploration Agency concur. Final numbers will come in a few days.

Regardless of whether or not 2011 breaks a record, here’s the important point: Scientists say human-driven climate change continues to help push Arctic sea ice on a disturbing three-decade downward slide.

“Is Arctic ice in a death spiral? Maybe not yet, but it’s in big trouble,” NSIDC director Mark Serreze tells ABC News.

Serreze points out that the five lowest amounts of Arctic sea ice on record (since 1979) have all been recorded in the last five years. And it’s not just the amount of ice, but the quality. It’s also getting thinner, making it more sensitive to increases in temperature.

So why should we care about Arctic sea ice?

–SEA LEVEL: Scientists tell us that Arctic sea ice acts as a giant air conditioner at the top of the planet, helping regulate the planet’s overall temperature. But as the white sea ice (which reflects a portion of the sun’s energy) melts, the darker water underneath absorbs energy, warming the water and creating a “feedback” that in turn, helps melt additional ice in a vicious cycle. Bcause it is already floating, this does not raise sea level much as it melts.

But in Greenland, it’s a different story. When ice calves off of Greenland’s glaciers, sea level rises. One recent study reported that Greenland glaciers lost 592 square miles of ice between 2000 and 2010. If Greenland melted entirely, global sea levels would rise about 20 feet.

–WEATHER: Scientists say ice loss may help alter weather patterns across the planet. The jet stream, for example, could shift further north. That could bring more frequent and intense droughts to the U.S. A jet stream change might also affect the path of storms and hurricanes. And more open water and heat could help supercharge those storms.

Many scientists believe human-emitted greenhouse gases warming the planet are already loading the dice toward a future with more weather extremes.

–WILDLIFE: Melting sea ice also bad news for a number of animals and organisms, including polar bears, who use the ice to hunt for food.

–OIL AND GAS EXPLORATION: Melting ice literally removes a major barrier to oil and gas exploration in a remote and harsh environment. For years, oil companies and nations have been fighting turf wars over who gets which part of the (potentially very lucrative) sea floor. Exxon, for example, just entered into a new Arctic exploration deal with the Russian government that could be worth tens of billions of dollars.

So what’s causing the ice to melt?

It has been well-established through several peer-reviewed scientific papers that Arctic sea ice loss cannot be explained by natural causes alone. One recent study from the National Center for Atmospheric Research found that roughly half of the Arctic sea ice decline from 1975 to 2005 can be blamed on increasing amounts of greenhouse gases.

Those same researchers were surprised by computer models that predict a 10-year period where the ice melt could pause, and the amount even increase, thanks to natural weather variability that is hard to predict.

That makes it tough to predict when the Arctic might go completely ice-free in summer. Indeed, one researcher, in this 2007 “World News” story by my colleague Bill Blakemore, predicts that an ice-free summer could come by 2012 or 2013.

The latest thinking among scientists has summer sea ice vanishing from the Arctic well before the end of the century, perhaps within the next 50 years. Given that greenhouse gases are only expected to increase between now and then, scientists do not see a reversal of sea ice declines in the near future.