After nearly two decades, Shell has received the final permission from the US government to begin Arctic oil drilling off the coast of Alaska. This comes ahead of President Barack Obama's visit to Alaska where he will examine environmental issues.

The area approved for drilling in the Chukchi Sea is estimated to contain about 15 billion barrels of oil, while the Arctic is thought to have more than 20 percent of the world's undiscovered oil and gas resources. Shell says drilling in the area could become a “game changer'' for US domestic production.

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“Activities conducted offshore of Alaska are being held to the highest safety, environmental protection, and emergency response standards,” said Brian Salerno, director of The Bureau of Safety and Environmental Enforcement (BSEE) which has approved the drilling.

While BSEE says its inspectors are present at the drilling rigs day and night to ensure safety, environmental groups strongly oppose Arctic offshore drilling. They claim that industrial activity will harm polar bears, Pacific walrus, ice seals and threaten whales which already suffer from global warming. The oil companies have not demonstrated they can clean up a spill in water choked by ice, the activists say, referring to the 2010 Deepwater Horizon oil spill disaster.

"Granting Shell the permit to drill in the Arctic was the wrong decision, and this fight is far from over," said Sierra Club executive director Michael Brune, according to USA Today. "The people will continue to call on President Obama to protect the Arctic and our environment."

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Shell had previously been allowed to begin drilling only the top sections of two wells in the Chukchi Sea, 8,000 feet below the ocean floor. With its last exploratory well drilled in 1991, the company obtained the leases in the Chukchi Sea in 2008. It has already spent some $7 billion on exploration there.

The energy major hopes to drill two exploratory wells during this year’s short open-water season as work has to stop in late September. Shell has two drilling vessels and about 28 support vessels in the Chukchi Sea. The company has just repaired an icebreaker which carries emergency well-plugging equipment.

President Obama is going to visit Alaska later this month, to speak at a conference on the Arctic and tour areas threatened by climate change.