Environment The world’s strangest sea-level shifts unfold off Japan’s coast

We often picture the ocean as flat and stable, but in reality its surface is uneven and constantly shifting. Off the coast of Japan, this hidden landscape has changed so dramatically that neighbouring stretches of sea are rising and falling at strikingly different rates. The reason is an unusual shift in the Kuroshio, one of the strongest currents on Earth, which has pushed warm water far from its normal path. This is remarkable because it has driven unprecedented ocean warming, altered long-established fisheries, and even intensified heatwaves and heavy rainfall on land, offering a rare and unsettling glimpse of how sensitive the ocean–climate system really is.

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The authors note that for an entire year and a half between April 2023 and August 2024, the region saw "intense marine heatwave conditions almost every day." And it was not just in the water: the Japan Meteorological Agency also found that the extreme ocean conditions contributed to record summer heat over land in northern Japan in 2023. Another group of scientists, meanwhile, linked the warm offshore current to extreme rainfall over Japan's Chiba Prefecture, near Tokyo, in September of 2023.

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