PETERSON AIR FORCE BASE, Colo. - U.S. and Canadian military commanders say they are examining their rescue capabilities in the Arctic as a shrinking ice cap brought about by climate change opens up rich oil and gas reserves and draws more commercial traffic to the top of the globe.

"There are a host of issues that face us as this beautiful part of the world opens up more and more," said U.S. Adm. James Winnefeld, commander of the U.S. Northern Command and the North American Aerospace Defence Command, or NORAD.

"And in order to be prepared for that, we have to keep our eye on the defence side of it, the security side of it, the environmental side of it, search and rescue, the safety side of it," Winnefeld said in a recent interview at his headquarters at Peterson Air Force Base, Colo.

Northern Command, formed after the Sept. 11, 2001, terrorist attacks, is responsible for defending the U.S. homeland and helping civilian authorities handle such emergencies as the Texas wildfires in April and the 2010 Gulf of Mexico oil spill. It provided aerial firefighting tankers, equipment airlifts and other assistance in those events.

NORAD is a joint U.S.-Canada command that defends the two countries from airborne threats and monitors maritime traffic off their shores.

Citing the Arctic's growing importance, the Pentagon announced in April that Northern Command would take on responsibility for military operations in the Arctic and Alaska. Previously, that responsibility was shared by the U.S. Northern, Pacific and European commands.

The summertime Arctic icecap has shrunk by about one-third since 1979, said Walt Mier, a research scientist at the National Snow and Ice Data Center at the University of Colorado. Some models predict that between 2040 and 2050, the Arctic could have no ice at all at some times of the year, he said.

The international Arctic Monitoring and Assessment Program made a similar projection in a report to be delivered next week to the Arctic Council, made up of the eight nations with Arctic territory.

Winnefeld and NORAD'S deputy commander, Canadian Forces Lt. Gen. Marcel Duval, said more ships in the Arctic Ocean -- and more jetliners crossing Arctic skies -- could mean more emergencies.

"More ships, more chances of accidents," Duval said in a separate interview in his office at NORAD headquarters at Peterson.

Last summer, the Canadian Coast Guard rescued 197 people from the cruise ship Clipper Adventurer, which ran aground inside the Arctic Circle.

Ice-free Arctic sea lanes could also be used by smugglers shipping drugs, guns and people, Winnefeld suggested in his blog last month.

Sea traffic is still light, with only about 25 ships a year currently crossing the maritime Arctic boundary between Alaska and the Yukon. But that number is increasing by 10 to 15 per cent a year, according to NORAD statistics.

Civilian air traffic over the Arctic is booming. U.S. and Canadian aviation agencies report more than 9,600 civilian flights across the North Pole in 2010, up nearly 21 per cent from 2008.

Arctic energy reserves also are attracting more attention as the US seeks to reduce its dependence on imported oil.

Shell Oil said May 2 it will apply to drill 10 wells off Alaska's Arctic shore in the next two years. Alaska's onshore reserves have diminished and the trans-Alaska pipeline now operates at less than one-third capacity.

The U.S. Geological Survey estimated in 2008 that the Arctic Circle has about 90 billion barrels of undiscovered oil, 1,670 trillion cubic feet of natural gas and 44 billion barrels of natural gas liquids. Combined, that would total 22 per cent of the world's undiscovered petroleum resources. About 84 per cent of those oil and gas reserves are estimated to be offshore.

If Northern Command is called on to help control an Arctic oil spill, weather and vast distances present formidable challenges, Winnefeld said.

"It takes about five times as long to do anything in the Arctic as it does anywhere else in the world just because the environment is so harsh up there," he said.

Duval, who served as a helicopter pilot in the Arctic, said he knows the challenges first-hand, recounting how he and his crew once refuelled their aircraft with hand pumps in minus-45-degree temperatures.

"So when people say ... it's difficult to do things in the Arctic, trust me, it is," he said.

NORAD says its fighters made 45 intercepts of Russian military flights between 2007 and 2010, compared with eight between 1999 and 2006. Duval told the Canadian Parliament last year the primary reason is that Russia's economy improved and its military budget grew.

He told The Associated Press those flights were training missions in international airspace and haven't given NORAD reason for concern.

"And to be frank, until it's proven to be a threat, it's not a threat," Duval said.

Few international conflicts have arisen in the Arctic in recent years, in part because of the work of the Arctic Council, comprising Canada, Denmark -- which also represents Greenland -- Finland, Iceland, Norway, Russia, Sweden and the United States, said Heather Conley, who studies Arctic issues for the Center for Strategic and International Studies.

"We're on a pretty good trajectory in the Arctic," Winnefeld said, adding it's important to keep relations good and avoid military competition there.

"Because none of us want to see that," he said.