A difference of just 0.5°C in global temperature rise from 1.5°C to 2°C can have significant impacts on society and ecosystems. The ocean has absorbed more than 90% of the heat generated by human activities, helping to slow the rise in land temperatures. However, increasing attention is being paid to ocean-related tipping elements, such as weakening ocean circulation and melting polar ice sheets, which raise serious concerns about our future.

The Japan Meteorological Agency, in collaboration with the Ministry of Education, Culture, Sports, Science and Technology, has published "Climate Change in Japan 2025," incorporating the latest observation results and scientific knowledge. The report is primarily intended to serve as basic information and evidence for climate change mitigation, adaptation, and impact assessments conducted by national and local governments. This article provides an overview of "Climate Change in Japan 2025" and introduces newly published information on ocean deoxygenation, a matter of concern regarding its impact on marine ecosystems.

The Kuroshio Large Meander, a large-scale ocean current meandering phenomenon occurring off the southern coast of Japan, continued for approximately seven years and nine months, from August 2017 to April 2025. This marked the longest meander on record. The occurrence of the large meander has had widespread impacts on climate, marine ecosystems, and fisheries, and reports have shown impacts on marine biological resources due to rising coastal water temperatures. Weather impacts have also been confirmed, including humid summers caused by marine heatwaves and increased precipitation. While the end of the large meander offers hope for future recovery of ecosystems and fisheries resources, ongoing global warming does not warrant optimism.