Sea surface temperatures (SSTs) around Japan have been unusually high repeatedly in recent years.
There have been persistent marine heatwaves, especially around northern Japan and in areas influenced by the Kuroshio current and its extension.
Some anomalies are linked with shifts in ocean currents (e.g. the Kuroshio extension’s meandering), which have moved warm water into areas that previously got cooler currents.
Here are some of the known or likely consequences:
1. Ecosystem stress and coral bleaching
In the Ryukyu Islands region, high-temperature events and anomalies have been correlated with coral bleaching.
As water temperatures rise and stay high, corals lose their symbionts, which can lead to mortality if stressful conditions persist.
2. Fisheries impacts
Shifts in what species are found in certain areas; warmer-water species moving north, which can disrupt established fisheries.
Possible economic effects for fishing communities that depend on species adapted to cooler waters.
3. Weather and climate effects
The marine heatwave around northern Japan in summer 2023 is believed to have contributed to unusually hot summers.
Changes in rainfall patterns: for example, the coastal warming off the Tokai–Kanto districts (related to the large meander of the Kuroshio) has been linked with increased summer rainfall over land in those regions.
4. Long‐term climate change risks
These anomalies are more likely under global warming; studies suggest that human‐caused climate change has doubled the likelihood of extreme ocean warming near Japan compared to preindustrial times.
If warming persists or intensifies, it could lead to more frequent/longer/more severe marine heatwaves, which ecosystems may struggle to adapt to.