Something unusual is happening in the oceans – and scientists are worried
The Earth's oceans reached their highest temperature ever recorded in modern history this past weekend. The average sea surface temperature in non-polar regions hit 21.1 degrees Celsius, breaking the previous record set in March 2024. Scientists are particularly concerned that this record was reached during a period when water temperatures are typically not at their peak.
The Earth's oceans reached their highest temperature ever recorded in modern history this past weekend. The average sea surface temperature in non-polar regions hit 21.1 degrees Celsius, breaking the previous record set in March 2024. For a system as vast as the oceans, even a seemingly small difference represents a significant change. Scientists are particularly concerned that this record was reached during a period when water temperatures are typically not at their peak, suggesting the possibility of further increases.
To understand the magnitude of this event, it is important to note that researchers are not measuring water temperature at a specific beach, but rather the average across vast areas of the world's oceans, excluding polar regions. On August 22, this average reached 21.1 degrees. This is the highest daily sea surface temperature recorded in the modern datasets of the European climate change service, Copernicus.
While the figure may not sound extreme to those accustomed to warm summer waters, calculating the average across such a large portion of the global ocean indicates that a massive amount of heat is being stored. The timing is the most unusual aspect: ocean surface temperatures typically peak around March and April, as summer ends in the Southern Hemisphere. The previous 2024 record was also set in March. The fact that this record was broken in August—a time when temperatures should be declining according to the normal seasonal cycle—is deeply concerning, especially as the El Niño phenomenon continues to develop.
Researchers attribute this phenomenon to two primary factors. The first is long-term global warming: greenhouse gas emissions from coal, oil, and gas cause more heat to remain in the climate system, with the oceans absorbing a significant portion of this excess. The second factor is El Niño, a natural climate phenomenon that warms vast areas of the Pacific Ocean and influences global weather patterns.
The issue is that El Niño is occurring while the oceans are already exceptionally warm due to long-term warming. Currently, about 42% of the world's ocean area is affected by marine heatwaves—periods where temperatures are significantly higher than normal for a specific location and season. This can have severe consequences, such as coral bleaching, mass mortality of marine life, and the disruption of ecosystems and fishing industries.
The oceans play a central role in regulating the Earth's climate, acting as a massive reservoir that absorbs excess heat and prevents the atmosphere from warming even faster. However, this heat remains in the water, contributing to sea-level rise through thermal expansion and providing more energy to weather systems. While some researchers suggest that current ocean heat levels are unprecedented in thousands of years, direct comparisons to pre-satellite eras are based on reconstructions from ocean floor sediments and fossils rather than direct measurements.
Scientists fear that this record may not be the final point. Abnormal temperatures were recorded throughout the months leading up to August, and as El Niño continues to strengthen, it may add further heat to the system in the coming months.
