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South Korea's surrounding seas are experiencing the most severe warming among global oceans, with sea surface temperatures rising three times faster than the worldwide average over the past decade, according to a recent analysis by South Korea's Meteorological Administration. Sea surface temperatures increased by 0.7 degrees Celsius during this period, compared to a 0.3-degree increase worldwide.

From 2016 to 2025, the Korea Meteorological Administration's marine weather stations recorded a 0.7-degree increase in sea surface temperatures around South Korea, while global average sea surface temperatures rose by 0.3 degrees. The recent ten-year average for the top four warmest years—2024, 2025, 2021, and 2023—occurred after 2021.

The concentration of heat in the ocean, known as "ocean heat content," also shows higher values for South Korea's surrounding waters compared to the global average. Marine heatwaves, which last for at least five days when sea surface temperatures exceed the 90th percentile of the annual mean, have increased by 3.7 times in recent years, from an average of 22.6 days per year to 83.3 days annually.

The intensity of these heatwaves has risen by 0.2 degrees Celsius compared to the annual mean. Off the coast of South Korea, the East Sea has shown particularly significant warming, with a 0.8-degree increase in sea surface temperatures over the past decade, 96.1 days of marine heatwave occurrences, and an intensity of 2.2 degrees.

The ocean heat content has risen by 0.56 gigajoules per square meter, more than double the global average. Despite efforts to reduce carbon emissions, this trend is expected to intensify in the future. According to the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) and regional climate change scenarios, sea surface temperatures in South Korea's surrounding waters are projected to rise above recent levels, even with carbon emissions reductions.

In the "low carbon" scenario (SSP1-2.6), sea surface temperatures could increase by 1.8 degrees by the late 21st century, while in the "intermediate" scenario (SSP2-4.5), they could rise by 2.2 degrees. Marine heatwaves are projected to increase by 181 days in the low carbon scenario and 231 days in the intermediate scenario compared to the recent ten-year period, with intensity increases of 0.7 degrees and 0.9 degrees, respectively.

Globally, sea surface temperatures are breaking new records, reaching 21.1 degrees Celsius recently, surpassing the previous high of 21.09 degrees Celsius (2024). This unprecedented rise in global ocean temperatures, typically seen in late spring, highlights the alarming acceleration of ocean warming.