Marine Heatwaves around Japan: The Role of Global Warming and Oceanic Variability
2026.05.25
Overview
Marine heatwaves are events in which ocean temperatures become extremely high for several consecutive days, causing major impacts on marine ecosystems and fisheries. This study shows that marine heatwaves around Japan are strongly influenced not only by long-term global warming but also by interannual-to-decadal variability in sea surface temperature. Our analysis demonstrates that removing this variability leads to a substantial reduction in marine heatwave occurrence, and further reveals that large-scale climate variability over the North Pacific plays an important role in shaping marine heatwaves around Japan.
Details
Marine heatwaves are characterized by extremely high-water temperatures typically persisting for several days to several months. Although they occur on relatively short time scales, elevated ocean temperatures can influence marine ecosystems and atmospheric conditions and may therefore be relevant to human society. Around Japan, the occurrence of marine heatwaves has attracted increasing attention in recent years, making it important to understand the background conditions under which these extreme events arise.
In this study, we analyzed daily sea surface temperature data based on satellite observations from 1983 to 2022, focusing on ten regions around Japan. We first examined the relationship between the recent increase in marine heatwaves and long-term global warming. When the long-term warming trend was removed from the sea surface temperature data for the period since the 2010s, the number of marine heatwave days decreased substantially. This result indicates that the recent increase in marine heatwaves around Japan is closely linked to background warming of the ocean.
However, sea surface temperature does not increase uniformly due to global warming alone. It also varies on interannual and decadal time scales. Although marine heatwaves occur over only several days to several months, their development can be influenced by these longer-term variations in ocean conditions.
To evaluate this influence, we next examined marine heatwaves using sea surface temperature data from which interannual-to-decadal variability had been removed. Using the same daily data and the same ten regions, we found that the number of marine heatwave days was greatly reduced when this variability was excluded. This result demonstrates that marine heatwaves around Japan are affected not only by long-term warming but also by changes in the background ocean state on interannual to decadal time scales.
In addition, we investigated the relationship between marine heatwaves around Japan and large-scale climate patterns over the North Pacific. Several climate modes defined from North Pacific sea surface temperature variability were found to influence marine heatwaves around Japan. In particular, one specific mode produced pronounced changes in the occurrence of marine heatwaves in the region.
Overall, this study shows that marine heatwaves around Japan occur under the combined influence of long-term warming and interannual-to-decadal variability in ocean conditions. From this perspective, understanding marine heatwaves requires considering how extreme short-term events are modulated by background changes across multiple time scales.
Publication Information
• Journal: Journal of Oceanography
• Title: Marine heatwaves around Japan over the past four decades: Links to interannual-to-decadal variability of sea surface temperature
(Please also include a Japanese translation if necessary)
• Authors: Yusuke Ushijima, Kei Sakamoto, Koji Yagi, Yuma Kawakami, Hiroki Togawa, Haruka Sasaki, Yoshikazu Fukuda
• DOI: 10.1007/s10872-026-00787-x
• URL: https://doi.org/10.1007/s10872-026-00787-x
Research Support
(Information on grants, funding programs, or other support)
This work was supported by JSPS KAKENHI Grant Numbers JP24H02227.
Contact Information
(Name) Yusuke Ushijima
Phone:+81899279833
E-mail: ushijima.yusuke.fp@ehime-u.ac.jp