National Geographic: Visitors to Japan’s northern island of Hokkaido venture onto drift ice near the coast of Shiretoko Peninsula. These free-floating pieces of ice, which annually travel about 620 miles (1,000 kilometers) from the Sea of Okhotsk, are the world’s southernmost Arctic sea ice. In recent years the amount of drift ice reaching Shiretoko has decreased noticeably, raising fears global warming will affect the local ecosystem and endanger winter tourism. (Read the full story.) Tatsuya …