The short version
- Average global sea surface temperatures reached 21.1C in August, surpassing the previous high recorded in March 2024.
- Scientists attribute the anomaly to decades of human-driven warming compounded by the current El Niño cycle, which is expected to strengthen through late 2026.
- Rising ocean heat poses significant risks including intensified extreme weather events, accelerated sea-level rise, and severe stress on marine ecosystems.
Global ocean temperatures have reached their highest level ever recorded, according to new data released by the European Copernicus Climate Change Service. The average surface temperature of the planet's seas, excluding polar regions, hit 21.1 degrees Celsius on a recent Saturday measurement. This figure narrowly exceeds the previous record of 21.09 degrees Celsius, which was established on three separate occasions during March 2024. The timing of this new peak is particularly unusual, as global sea temperatures typically reach their annual maximum in March or April, coinciding with the end of summer in the southern hemisphere.
The deviation from seasonal norms highlights the severity of current thermal conditions. August is generally a period when ocean heat content stabilizes or begins to decline in many regions, yet the waters remain far above average for this time of year. Dr. Samantha Burgess, deputy director of Copernicus, described the record as a clear signal that the oceans are under increasing stress. She emphasized that while the El Niño weather phenomenon is contributing additional heat to the system, it is acting upon a baseline already elevated by decades of human-driven climate change.
The data underlying these conclusions comes from measurements taken approximately 10 meters below the surface. These figures are compiled using a combination of observations from buoys, ships, and satellites to produce a comprehensive global estimate. While scientists acknowledge that any global average carries inherent uncertainties and the margin by which the record was broken is small, the consistency of the warming trend is significant. The southern hemisphere, which contains a larger volume of ocean water than the north, exerts a dominant influence on these global averages, making the current readings especially notable.
El Niño plays a critical role in this thermal surge by bringing unusually warm waters to the surface of the eastern and central tropical Pacific Ocean. This phenomenon is expected to continue strengthening until around Christmas time, with forecasts suggesting it could become the strongest event in centuries. As El Niño intensifies, global average temperatures typically spike due to the vast area of warmer water releasing heat into the atmosphere. Consequently, ocean temperatures are projected to climb even further into 2027 if current trends persist.
The warming is not confined to the Pacific regions directly associated with El Niño. Large areas of seas surrounding the United Kingdom and Europe have experienced marine heatwave conditions for much of the year. This widespread warmth serves as evidence of the growing influence of human-caused climate change on global oceans. The seas absorb more than 90 percent of the excess heat trapped by greenhouse gas emissions, primarily resulting from the burning of fossil fuels. This capacity to store heat has masked some atmospheric warming but has created severe challenges for marine environments.
The consequences of hotter oceans extend beyond temperature metrics. Warmer seas provide storms with additional moisture and energy, potentially supercharging extreme weather events. In coastal regions, elevated sea temperatures can intensify land-based heatwaves by reducing the cooling effect typically provided by sea breezes. Furthermore, thermal expansion causes warmer water to occupy more space, contributing to rising sea levels and increasing the risk of coastal flooding. These physical changes compound the dangers faced by vulnerable communities located near shorelines.
Marine ecosystems are also bearing the brunt of this thermal stress. Intense ocean heat is devastating for sensitive habitats such as coral reefs, which are highly susceptible to temperature fluctuations. The increasing frequency and duration of marine heatwaves are placing unprecedented pressure on marine biodiversity and the human communities that depend on these resources for food and livelihoods. Scientists warn that the combination of long-term warming trends and acute weather phenomena like El Niño creates a compounding risk for ocean health.
Looking ahead, the trajectory of ocean temperatures remains a key indicator of broader climate impacts. With El Niño still some way from its expected peak, further temperature increases are likely in the coming months. The data suggests that without significant reductions in greenhouse gas emissions, the oceans will continue to absorb excess heat, leading to more frequent and severe marine heatwaves. Monitoring these changes is essential for understanding the evolving climate landscape and preparing for the associated environmental and societal challenges.
Sources behind this briefing
Go to the original reporting
- BBC Science & Environment↗World's oceans hit highest temperature on record as El Niño grows
