Global ocean temperatures hit record high

August 25, 2026

The world’s oceans have reached their highest recorded surface temperature, providing another alarming sign of the accelerating climate crisis and its growing impact on marine ecosystems, coastal communities and global weather patterns.

According to the latest climate data, the average sea surface temperature across oceans outside the polar regions climbed to 21.1°C, setting a new record. The extraordinary level of ocean warming comes as the planet experiences widespread heatwaves, wildfires, droughts and extreme rainfall.

Scientists say the surge in marine temperatures reflects both long-term human-caused climate change and the additional warming associated with a rapidly developing El Niño.

Oceans absorb most of the planet’s excess heat

The oceans play a crucial role in regulating Earth's climate. More than 90% of the excess heat trapped by greenhouse gases is absorbed by the world's oceans.

While this has slowed the rate at which temperatures rise in the atmosphere, it has also placed enormous pressure on marine environments.

As fossil fuels such as coal, oil and natural gas are burned, increasing concentrations of carbon dioxide trap additional heat in the climate system. Much of that energy eventually accumulates in ocean waters.

Persistent ocean warming can contribute to rising sea levels, stronger storms, marine heatwaves and widespread disruption of ecosystems that millions of people depend on for food and income.

El Niño adds to record ocean warming

The latest temperature spike is being intensified by a developing El Niño, a natural climate phenomenon associated with unusually warm waters in parts of the tropical Pacific Ocean.

El Niño can temporarily increase global temperatures while significantly altering rainfall and weather patterns around the world.

The developing event has already been associated with weather disruptions in several regions, including reduced monsoon rainfall in India, severe wildfire conditions in Indonesia and increased concerns about fire risks in Australia.

Its arrival comes on top of decades of greenhouse gas-driven warming, increasing the likelihood of additional temperature records and extreme weather events.

August ocean heat record is particularly unusual

The timing of the new global ocean temperature record makes the development especially significant.

Sea surface temperatures typically reach their annual global maximum during March and April, following summer in the Southern Hemisphere. Because the Southern Hemisphere contains substantially more ocean than the Northern Hemisphere, its seasonal warming has a major influence on global averages.

Reaching record temperatures during August therefore highlights the exceptional amount of heat currently stored in the oceans.

Dr Samantha Burgess of the EU's Copernicus Climate Change Service (C3S) described the record as another indication that the world's oceans are experiencing increasing pressure.

Marine heatwaves are also becoming significantly more common. According to C3S data, the number of marine heatwave days worldwide has increased more than threefold compared with the early 1990s.

Hotter oceans increase sea level rise

Rising ocean temperatures directly contribute to global sea level rise.

As seawater becomes warmer, it expands through a process known as thermal expansion. Combined with melting glaciers and ice sheets, this increases ocean levels and raises flooding risks for coastal cities and low-lying island nations.

Even relatively small increases in average sea level can make storm surges more destructive, particularly during hurricanes, typhoons and other severe weather events.

With billions of people living in coastal regions, continued ocean warming could significantly increase economic and humanitarian risks.

Warmer seas can fuel more extreme weather

Hotter oceans can also provide additional energy for storms.

Warm seawater increases evaporation, transferring both heat and moisture into the atmosphere. Under favorable atmospheric conditions, this additional energy can intensify heavy rainfall and strengthen tropical storms.

The latest ocean temperature record comes during a period of widespread extreme weather. Parts of Europe and North America have experienced severe heatwaves, drought conditions and wildfires, while regions of Asia have faced intense rainfall and powerful typhoons.

Although individual weather events have multiple causes, scientists warn that rising global temperatures are increasing the conditions that can make many extreme events more intense.

Ocean warming could weaken a major carbon sink

The oceans do more than absorb heat. They also remove a significant portion of the carbon dioxide produced by human activities, including fossil fuel combustion and deforestation.

This natural carbon absorption has helped slow the accumulation of CO2 in the atmosphere.

However, warmer seawater generally becomes less effective at absorbing carbon dioxide. Continued ocean warming could therefore weaken one of Earth's most important natural mechanisms for limiting atmospheric CO2 concentrations.

Such a decline could create an additional challenge for global efforts to control climate change.

Marine ecosystems face growing pressure

Record ocean temperatures also pose serious threats to marine biodiversity.

Prolonged periods of unusually warm water can trigger marine heatwaves, damaging coral reefs, kelp forests, fisheries and other critical habitats.

Corals are particularly vulnerable. Extended exposure to elevated temperatures can cause coral bleaching, during which corals expel the algae that provide much of their energy. Severe or repeated bleaching events can eventually lead to widespread coral mortality.

The consequences extend beyond wildlife. Healthy marine ecosystems support fisheries, tourism, coastal economies and food security for communities around the world.

Protecting marine ecosystems becomes more urgent

Brian O’Donnell, director of Campaign for Nature, said tackling record ocean warming requires both rapid reductions in fossil fuel emissions and stronger protection for marine and coastal environments.

Ecosystems such as mangrove forests, salt marshes and kelp beds can capture and store carbon, while coral reefs and other coastal habitats can provide natural protection against waves and storms.

More than 190 governments have committed to protecting and conserving at least 30% of the planet by 2030, making effective marine conservation an increasingly important part of global climate and biodiversity strategies.

However, scientists emphasize that conservation measures alone cannot stop ocean warming. Significant reductions in greenhouse gas emissions remain essential for limiting long-term temperature increases.

Record ocean heat signals growing climate pressure

The Copernicus dataset covers oceans outside the polar regions and extends back to 1979, when satellite observations began providing increasingly reliable global measurements.

The figures do not include the Arctic, which is warming substantially faster than the global average.

The latest ocean temperature record adds to growing evidence that climate change is reshaping the world's oceans. As marine heat continues to accumulate, the consequences could increasingly affect sea levels, weather extremes, biodiversity, fisheries and coastal communities.

Reducing greenhouse gas emissions while expanding effective protection and restoration of marine ecosystems will be critical to limiting those risks in the decades ahead.