Over the past 58 years, surface water temperatures around the Korean Peninsula have risen by 1.6 degrees. That increase is more than double the global average, indicating a faster pace of ocean warming here than in other regions.

According to the ‘2026 Climate Change Impact Briefing Book for the Marine and Fisheries Sector’ released on the 21st by the National Institute of Fisheries Science, over the past 58 years (1968~2025) surface temperatures around the Korean Peninsula rose by 1.6 degrees, more than twice as fast as the global average (0.76 degrees). In particular, the rate of increase over the most recent 10 years was about three times the earlier level, clearly showing an acceleration of ocean warming.

From 1968 to 2025, the long-term warming rate was 0.0276 degrees per year, whereas over the most recent decade, 2016 to 2025, it reached 0.09 degrees per year.

The institute explained, “This is the result of a strengthening of the Tsushima Warm Current; an increase in the number of heatwave days caused by the expansion of high-pressure systems in summer; and a rise in the intensity and frequency of marine heatwaves (a phenomenon in which sea temperatures remain unusually high compared with past observations).”

In fact, the number of days under heatwave advisories (daily maximum temperature of 33 degrees or higher) has been rising from an average of 11.0 days in 1991~2020 to 14.2 days in 2023, 30.1 days in 2024, and 29.7 days last year.

Clear changes are also being detected across the marine ecosystem. Across all waters around the Korean Peninsula, ocean acidification is underway. Due to enhanced stratification driven by ocean warming, dissolved oxygen in the deep layers of the East Sea is declining, and surface nutrients also tend to decrease.

Enhanced stratification refers to a phenomenon in which warming of the upper ocean increases the density difference between surface and deep waters, the two layers mix poorly, and vertical mixing weakens.

Due to increased summer downpours and the prolonged cold-water zone in the southern East Sea (the appearance in summer of seawater at least 5 degrees cooler than surrounding waters), harmful red tides occurred for the first time in six years, and the subtropical blue umbrella jellyfish spread beyond Jeju to the East Coast, indicating that the emergence patterns of harmful organisms associated with climate change are diversifying.