On Wednesday, the Ninth Circuit Court of Appeals ruled that the Department of the Interior’s environmental review of drilling leases for the Arctic is unsound. The court ruled that the Interior’s estimate of one billion barrels of recoverable oil from the Arctic Ocean was “chosen arbitrarily,” and said the department had examined “only the best case scenario for environmental harm, assuming oil development,” according to the decision.

The Interior Department based its assessment of environmental impacts on a one billion barrel estimate for recoverable oil, although the court notes in its decision that the Bureau of Ocean Energy Management estimates the amount could reach up to 12 billion barrels.

“A best case scenario ‘skew[s]’ the data toward fewer environmental impacts, and thus impedes a ‘full and fair discussion of the potential effects of the project,’” the ruling states. But while the court’s decision will require the Interior Department to reevaluate all of its 2008 Arctic lease sales, it does not directly address whether companies with existing leases can continue drilling, The Hill reports.

Lease Sale 193 was originally held during the Bush administration era in 2008. In 2010, the Alaska Federal District Court determined that the original lease sale violated the National Environmental Protection Act. However, during the following year, the Obama administration reaffirmed the decision to lease millions of acres of Arctic Ocean to oil companies.

In 2012, a coalition of groups including Earthjustice, the Center for Biological Diversity, and the Alaska Wilderness League filed an appeal with the Ninth Circuit Court challenging the approval of Lease Sale 193 due to wide gaps in it environmental review.

“Even though this critical missing information prevents adequate analysis of the effects of drilling in the Chukchi Sea,” Earthjustice said, “the administration concluded that none of it, including information about what areas are important to species such as bowhead whales, walrus, and beluga whales, is essential to the lease sale decision.”

“The Bush-era lease sale in one of the most fragile and least understood ecosystems in the world was never a good idea,” the 2012 appeal states. “The Obama administration’s decision to affirm Chukchi Lease Sale 193 in America’s Arctic Ocean was a clear case of politics trumping science. Right now, Shell Oil’s drill ships are on their way to the Chukchi Sea to begin the most aggressive course of Arctic drilling in history, despite the fact that we still know so little about the impacts this drilling could have on the Arctic’s marine environment.”

Shell Oil Company lobbied federal officials for years to be allowed to drill in the Arctic, and the company has invested nearly $5 billion in leases and equipment for drilling, the New York Times reports. But in early 2013, the company announced it would be taking a “pause” in drilling in the Arctic due to a series of costly errors and accidents. Two drill ships suffered serious damage as they were leaving the Beaufort and Chukchi Seas in 2012.

“Shell – one of the world’s largest companies – has so far spent $5 billion on this perilous Arctic folly,” Greenpeace Arctic Campaign Leader Gustavo Ampugnani said in a press release. “As the whole world watched, their bold Arctic expedition in 2012 became a global laughing stock as giant rigs broke fee from their moorings and beached on Alaskan shores, dire storm warnings were ignored, and multiple health, safety and environmental regulations were breached.”

Even so, Shell has been pushing to resume drilling. The company submitted a revised Chukchi Sea exploration plan to the Department of the Interior in November. Of the companies that received leases in 2008, Shell is the only one to have begun drilling operations in the Arctic. Erik Grafe, an attorney for Earthjustice told The Hill that other oil companies are hesitant to begin drilling because the lease sales have twice been questioned.

“Drilling for oil in the Chukchi Sea poses an enormous risk to the region’s people and wildlife,” Ampugnani said. “It locks us into a dangerous and dirty fossil fuel future, and it pushes us far closer to global climate catastrophe and the imminent hazards of extreme weather.”

The coalition that challenged Lease Sale 193 includes Alaska Native groups as well as conservation groups, and is represented by Earthjustice.

Alisha is a writer and researcher with Ring of Fire. You can follow her on Twitter @childoftheearth.