The Japan Meteorological Agency announced, on May 15, 2007, the results of its research on how the surface temperatures of Japanese waters have changed over roughly the past 100 years (1900-2006). The yearly average surface temperatures of Kyushu and Okinawa waters, of central and southern parts of the Sea of Japan, and of waters to the south of Honshu have risen at a rate of 0.7 to 1.6 degrees Celsius per 100 years. This is 1.4 to 3.2 times larger than the world average (warming at a rate of 0.5 degrees Celsius per 100 years).

Compared to the warming rate of mean Japanese land surface temperatures over the same period (+1.1 degrees per 100 years), the rate of sea surface temperature is almost same in the Yellow Sea and East China Sea, the southern part of the Sea of Japan, waters to the south of the Kanto area, and the northern part of waters off the coast of the Shikoku and Tokai areas; smaller in the waters around the Sakishima Islands and the southern part of waters off the coast of Shikoku and Tokai areas (+0.7 to 0.8 degrees per 100 years); and larger in the central part of the Sea of Japan (+1.6 degrees per 100 years).

Regarding seasonal trends in long-term changes in sea surface temperatures, warming rates are largest in winter (from January to March) or autumn (from October to December).