A US-Canadian move to block new leases for oil or gas drilling in sovereign Arctic waters is designed to protect an area already severely disrupted by climate change.

A quick tour of the Arctic and what is at stake:

- THE ARCTIC -

The Arctic Circle, which starts 66.5 degrees north of the equator, marks an area where on at least one day of the year there will be no light or no night -- and that period is longer, the further north you go.

It covers more than 20 million square kilometres (7.7 million square miles), an area bigger than Russia, cutting through northern Canada, Alaska, Russia, Scandinavia and Greenland. About a third of the area is land.

The part of the Arctic Ocean permanently covered by ice has been diminishing steadily for several decades due to global warming, making the region more accessible to shipping, and thus oil and gas extraction.

The record low ice cover -- 3.41 million square kilometres in September 2012 -- was 44 percent below the 1981-2010 average.

Some of the ocean falls under the national jurisdictions of the countries it borders, but most is not subject to any national laws or regulations.

An Arctic Council created in 1996 to address territorial and political disputes has so far only dealt with peripheral issues such as protocols for sea rescue and oil spills.

- ENVIRONMENTAL RISKS -

The biggest threat -- driven by the burning of fossil fuels -- is climate change, which has pushed temperatures in the Arctic up twice as fast as the worldwide average.

Scientists have calculated that global oil, gas and coal projects already under construction or in operation will push Earth past the threshold of dangerous global warming, heating the planet by more than two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial era levels.

Developing even a portion of the Arctic's massive as-yet-untapped gas and oil reserves would exacerbate climate change even further.

The region's human communities and wildlife -- from polar bears to bowhead whales, from seals to sea birds -- are also at risk.

Dozens of distinct indigenous cultures within the Arctic depend directly on the ocean and its wildlife for food and income.

Oil production, and spills, difficult to clean up in icy conditions, could threaten livelihoods by damaging fragile ecosystems. Dirty fuel from ships operating in the Arctic is also a source of pollution.

Climate change, meanwhile, has already had a major impact on these mostly coastal communities, some of which are literally falling into the sea.

- NOT ON THE SAME PAGE -

The US decision designates the vast majority of its waters in the Chukchi and Beaufort Seas -- an area covering some 50 million hectares (125 million acres) -- as "indefinitely off limits" to offshore oil and gas leasing. Canada said all its Arctic waters were off limits.

Both the United States and Canada have aggressively developed other fossil fuel resources in the last two decades -- gas extracted via "fracking" and oil from tar sands, respectively.

The same is not true for Russia and Norway, whose economies depend heavily on oil, some of which is taken from the Arctic Circle.

"The economy-energy balance of the US is not the same as for Russia and Norway," notes Laurent Mayet, France's representative to the Arctic Council.

- NOT WORTH THE TROUBLE? -

In September 2015, Anglo-Dutch oil giant Shell abandoned exploratory drilling operations in the Alaskan Arctic, saying not enough oil and gas had been discovered to make extraction worthwhile. The licence had been granted by the Obama administration.

The British company Cairn Energy likewise gave up on its forays, said Pierre Terzian, head of French consulting firm Petrostrategies.

"There were no imminent prospection projects" before the joint US-Canadian announcement, Terzian told AFP. "Why go into the Arctic when there is plenty of oil and gas elsewhere that is technically less expensive to extract and does not carry as much risk in terms of image?"

French group Total has gone further, renouncing the exploitation of oil fields in the Arctic.

"The best insurance for the Arctic is a low price for oil," Terzian added.

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