A federal appeals court has sided with a challenge to oil drilling off Alaska’s northwest coast. A coalition of native and environmental groups had objected to the U.S. government’s authorization of oil and gas projects in the Chukchi Sea, warning of threats to sea life and contamination of the ocean. In a ruling this week, the U.S. Court of Appeals for the 9th Circuit said the government performed an inadequate assessment of the potential environmental impact that used only the “best case scenario.” The ruling could jeopardize the oil giant Shell’s plan to resume drilling operations in the Arctic this summer. Shell previously suspended its drilling after a series of mishaps. In a joint statement, the plaintiffs in the case called the ruling “a victory for the Arctic Ocean,” adding: “We should not have to depend on courts to protect our oceans. President Obama must now take seriously his obligation to re-think whether and under what conditions to allow risky industrial activities in the Chukchi Sea.”