NIFS said that the average sea surface temperature (SST) in East Asian waters around S. Korea reached 20.84℃ in 2025, the second-highest level since the records began in 2000. Korean waters also averaged 17.66℃, higher than usual. 

The monthly data showed water temperature broadly in line with the 2001-2020 average from January to May, but from June to October the average jumped to 26.44℃, setting a new seasonal record. 

The observation results from research vessels (R/Vs) operating in S. Korea’s exclusive economic zone (EEZ) since the 1960s showed that the second half (August - December) of 2025, SST averaged 21.27℃, - the second-highest on record after 2024’s annual average of 22.28℃. 

The primary driver of the unprecedented high SST in East Asian waters including S. Korea last year was: the early expansion of the North Pacific high pressure; prolonged heat linked to the Tibetan high from late July; and increased inflows of warm, low-latitude waters from the Tsushima Current extending from summer into autumn. 

NIFS president Choi, Yong-seok said, “Climate observation data tells that the rate of temperature rise in the seas around S. Korea is extremely steep. To embrace climate challenge, NIFS will step up its research on climate forecasting and comprehensive adaptation technologies for the fisheries sector.”