Government scientists believe Alaska's North Slope has huge deposits of frozen natural gas that current technology could extract, according to an Interior Department report.

The study by scientists at Interior's U.S. Geological Survey estimates that more than 85 trillion cubic feet of natural gas in the form of gas hydrates — methane gas locked in water as an ice-like solid — eventually may be recoverable from Alaska's North Slope, both on shore and in coastal waters.

The abundance of methane hydrates in nature, both in the Arctic region and in ocean sediment has been known for decades. The study released Wednesday is the first assessment of the largest U.S. technically recoverable concentration of gas hydrates.

The report cautioned, however, that further research including long-term production tests will be needed to determine whether such development will be economical.

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Scientists also are uncertain about what impact the disruption of the frozen methane gas may have on global warming.

Scientists are concerned that if the gas-hydrates are disturbed it could result in a large release of methane into the atmosphere. Methane is 21 times as potent a greenhouse gas as carbon dioxide.

Nevertheless, said Interior Secretary Dirk Kempthorne, the new assessment "points to a truly significant potential for natural gas hydrates" as a clean-energy resource.

The country uses about 23 trillion cubic feet of natural gas annually, according to the Energy Information Administration.

Kempthorne dismissed the concern over the possible impact on climate.

He said developing gas hydrates in a controlled manner "is no more riskly than in a conventional gas field" and that in many cases "the hydrates we're talking about [are] relatively deep underground, isolated, insulated from the surface changes."

The recoverable gas-hydrates would be nearly three times the estimated 30 trillion cubic feet of conventional natural gas estimated to be commercially available on Alaska's North Slope if a way is found to bring it to the lower 48 states.

A proposed natural gas pipeline is at least a decade away and its construction is not a certainty.

Even if a pipeline were built, energy companies would almost certainly pursue conventional natural gas development long before they show any commercial interest in methane hydrates.

But Mark Myers, director of the U.S. Geological Survey, said it's important to understand the potential of gas hydrates as a major energy resource.

He said there now is "a growing body of evidence" indicating that gas hydrates in conventional hydrocarbon reservoirs of the North Slope "can be produced with existing technology."

A promising method of extraction would involve lowering the pressure within an accumulation of hydrates so that the solid hydrates are changed into water and methane gas that can be brought to the surface, the study said.

The study assessed a broad area across the expanse of Alaska's North Slope including both onshore areas and waters up to three miles from land.