Shifting Memories of the Sea: Global Warming and Ecosystem Changes in Japan’s Coastal Waters (May 2007–July 2023)

Shifting Memories of the Sea: Global Warming and Ecosystem Changes in Japan’s Coastal Waters (May 2007–July 2023) Over the past 100 years, sea surface temperatures in Japan’s coastal waters have risen by 1.28°C, significantly exceeding the global average of 0.61°C. In particular, abnormally high temperatures—5°C above average—were observed off the coasts of Tohoku and Hokkaido in July 2023. In Tateyama City, Chiba Prefecture, a rise of approximately 5°C over the past century is estimated, and coral bleaching is becoming increasingly severe in the Nansei Islands. As a result of these changes, mackerel populations have declined while horse mackerel have increased in Wakayama Prefecture; in the Tsugaru Strait, Aomori Prefecture, the growth of Macrocystis pyrifera has deteriorated, leading to the progression of the “isoyake” phenomenon. Off the coast of Oma, cold-water seaweed has declined, and the impact on fisheries is expanding. In the Seto Inland Sea, nori cultivation has become difficult, and the occurrence of red tides during the winter has increased. Going forward, it is predicted that sea surface temperatures will rise by up to 3.6°C by the end of the 21st century due to climate change, and there are concerns about the impacts of stronger typhoons and sea level rise. Reducing greenhouse gas emissions and monitoring the marine environment have become urgent priorities.