The U.S. Department of the Interior has approved Shell Oil’s plan to respond to an oil spill in the Arctic’s Beaufort Sea, clearing the way for exploratory drilling this summer. The decision follows similar U.S. government approval for a spill response plan in the Chukchi Sea, and Shell said that separate exploratory drilling ships will begin working in the two seas off Alaska when ice melts this summer. Shell’s response plan calls for the exploratory vessels to be accompanied by more than a dozen ships that will carry oil-soaking skimmers and booms, as well as a capping stack that could be lowered into the ocean to control a blowout. The Interior Department estimates that 26.6 billion barrels of recoverable oil and 130 trillion feet of natural gas lie under the continental shelf off Alaska. But environmental groups criticized the Interior Department for approving Shell’s spill response plans, saying there is no viable way to clean up an oil spill in the extreme, icy conditions of the Arctic Ocean.