An aerial view shows an ice-free Shiretoko Peninsula in summer, covered in lush vegetation. Most of the peninsula is a national park that was listed as a UNESCO World Heritage site in 2005.

Seasonal drift ice from the Sea of Okhotsk carries nutrients that spur biodiversity around Shiretoko. But a 2007 report from the Japan Meteorological Agency noted a "gentle tendency toward a decrease in the amount of ice" forming in the sea.

"We don't know yet if this is due to global warming," said Keiji Hamada, a scientific officer with the agency.

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