OSLO, Feb 4 (Reuters) - Norway may restrict oil firms' access to offshore resources in the Arctic by moving the so-called ice edge, a line that sets a legal limit on the extent to which companies can go north in search of oil.
The ice edge is a legally drawn boundary that is meant to approximate the constantly changing southern fringe of the permanent ice sheet. Anything north of that legal line is off-limits to oil drilling under Norwegian law.
However, instead of redrawing the line further north to reflect the retreating ice sheet, the ruling coalition may move it further south as it responds to political pressure to extend the environmental protection of the Arctic.
The ice cover in the Barents Sea has halved over the past 40 years. In practice, it would be ice-free year-round by 2050 given the current trend, Tor Eldevik, a professor at the Bjerknes Centre for Climate Research at the University of Bergen told Reuters.
"It's one of the difficult issues (for the government to decide on)," Prime Minister Erna Solberg told Reuters in an interview.
"The ice cap is moving, it's been moving upwards ... You can't measure it every year, so you have to put the line, and have a discussion where that line would have to be."
"If you take it too far down then it would cross some areas that are already being explored."
The center-right minority government has been reviewing the ice edge boundary and is due to present its new demarcation line to parliament in April. It has already received a recommendation from an advisory group of Norwegian research institutions and state agencies, which have presented two options.
One would be to draw the line where the sea ice appeared at least 30% of the time in April, the peak month for the Arctic ice sheet in the Barents Sea, between 1988 and 2017.
That would place the line further north than today, as the current line, set in 2006, was based on sea ice observations from 1967 to 1989.
The other option is to draw the line at where sea ice probability is only 0.5%, in order to protect the Arctic environment. This would place the line further south and would be problematic for oil and gas companies, Norway's biggest industry.
It would affect at least eight oil exploration licenses operated by Equinor, Aker BP and Spirit Energy, majority-owned by Britain's Centrica, the Norwegian Oil and Gas Association (NOG), a lobby group, said.
It would also come close to the Wisting discovery estimated to hold 440 million barrels of oil. Equinor plans to develop the discovery together with OMV, Idemitsu Petroleum and Petoro, a Norwegian state-owned firm.
"The sea ice influences the ecosystem that lies further south ... and this is why some think that it should be further south than it has been before," said Cecilie von Quillfeldt, a senior adviser at the Norwegian Polar Institute.
The NOG is proposing a third option: to use a "dynamic" ice edge definition, meaning that the line would move along with observable sea ice, and is not set as "a static and politically determined line on the map".
Lawmakers Reuters spoke to said the most likely deal would be moving the line further south than now, but without affecting oil licenses already granted to companies.
"None of the extremes would gain enough support. The line would be put somewhere in the middle," Lene Westgaard-Halle, a Conservative lawmaker on parliament's energy and environment committee, told Reuters.
An opposition lawmaker, speaking on condition of anonymity, said such a compromise would be acceptable. However, pro-green lawmakers in all parties are enjoying popular support and could be successful in pushing for the ice edge definition that goes the most south.
Waters close to the ice sheet are important feeding grounds for many Arctic species, from tiny zooplankton to polar bears and whales. At the same time, the Barents Sea may contain two-thirds of the oil and gas yet to be discovered off Norway, according to Norwegian official estimates.
(Editing by Gwladys Fouche, Mark Bendeich and Peter Graff)