Korean seas warming twice as fast as global average

The waters surrounding South Korea are experiencing ocean warming at an alarming rate, significantly outpacing the global average. According to the Korea Meteorological Administration (KMA), sea surface temperatures around the Korean Peninsula have risen by 0.7 degrees Celsius over the past decade, more than double the global increase of 0.3 degrees Celsius. This accelerated warming trend has led to a dramatic increase in marine heatwave days, which have surged 3.7-fold in the last ten years compared to the 1991-2020 average.

The KMA's analysis, based on data from marine weather buoys and global sea surface temperature records from 2016 to 2025, reveals a concerning acceleration. While sea surface temperatures around Korea increased by approximately 0.3°C per decade since 1991, the most recent 10-year period saw an increase of 1.2°C. The four warmest years on record for sea surface temperatures around Korea have all occurred within the last five years, with 2024 being the highest.

Ocean heat content, a measure of the heat stored in the ocean, has also increased more rapidly around the Korean Peninsula than in the global ocean. Marine heatwaves, defined as periods where daily sea surface temperatures remain at or above the 90th percentile of historical temperatures for at least five consecutive days, are now occurring for an average of 83.3 days per year, up from 22.6 days historically. Their intensity has also increased, with temperatures during these events averaging 2.1°C above normal.

The East Sea, also known as the Sea of Japan, is particularly affected. Its average sea surface temperature over the past decade was 0.8°C above the long-term average, and marine heatwaves occurred for an average of 96.1 days per year with an intensity of 2.2°C above normal. Ocean heat content in the East Sea has risen by 0.56 gigajoules per square meter, more than double the global ocean increase. These findings paint a stark picture of the escalating impact of climate change on regional marine ecosystems, even under scenarios with reduced greenhouse gas emissions.