"We will of course claim what is ours under international law," she said. "But we know that leaves a great vast amount of the Arctic that will be a common responsibility."Last year in Greenland, Clinton and her counterparts from other nations took a small step toward international cooperation by agreeing to coordinate Arctic search-and-rescue missions for stranded sailors and others. Officials are now trying to enhance the cooperation, including through joint plans to prevent oil spills in an environment that would make cleanup a logistical nightmare. And the U.S. has also been championing measures such as shifting away from dirty diesel engines, agricultural burning and hydrofluorocarbons to lessen the effect of short-lived greenhouse gases that are a particularly potent source of climate change in the Arctic.