1217. Record-high Sea Surface Temperatures and Sea Level Rise

The oceans, which cover about 70% of the Earth's surface, play an important role in climate regulation and are also carbon sinks. Oceans store 90% of the excess heat from greenhouse gases such as carbon dioxide and methane emitted by humans.

According to a paper published in Nature, global sea surface temperatures have been at record levels for more than a year since April 2023, averaging 0.25 °C higher from April 2023 to March 2024 than the previous record in 2015-2016. This level of rise represents a roughly once-in-512-year event under the current long-term warming trend. While the authors conclude that the record-breaking surge in sea surface temperatures in 2023-2024 would have been virtually impossible without a global warming trend, they suggest that it is not at a level beyond what models can simulate and that sea surface temperatures are expected to return to the long-term warming trend in the future.

On the other hand, on March 13, NASA announced that the rate of sea level rise will be higher than expected in 2024, the hottest year on record. According to a NASA-led analysis, the rate of sea level rise last year was 0.23 inches (0.59 centimeters) per year, higher than the expected rate of 0.17 inches (0.43 centimeters) per year. In recent years, about two-thirds of sea level rise has been due to melting ice sheets and glaciers that let water into the ocean from land. About one-third has been due to thermal expansion of ocean water. However, in 2024, that contribution reversed, with thermal expansion now accounting for two-thirds of sea level rise. The annual rate of sea level rise has more than doubled since satellite records of sea level height began in 1993. Since 1993, global sea levels have risen a total of 4 inches (10 centimeters).

(References)
Jens Terhaar et al, Record sea surface temperature jump in 2023–2024 unlikely but not unexpected, Nature (2025). https://www.nature.com/articles/s41586-025-08674-z

Contributor: IIYAMA Miyuki, Information Program