The Ocean Is Running a Fever: Marine Heatwaves Now Cover 82% of the Global Ocean 

Global sea surface temperature anomaly (June 2026). The map shows deviations in sea surface temperature from the long-term average, with widespread above-average ocean temperatures (red/orange areas) observed across many regions, highlighting continued ocean warming and the persistence of marine heat extremes.

Credit: Mercator Ocean International / Copernicus Marine Service (CMEMS). Data: GLO12.  

The global ocean has reached its warmest temperature ever recorded for this time of year. On 21 June 2026, the Copernicus Marine Service measured a global average sea surface temperature of 21.0°C (around 0.7°C above the long-term average of approximately 20.3°C for late June). Copernicus Climate Change Service (C3S) independently recorded 20.86°C (around 0.6°C above its long-term average), with both setting new daily records.  

Although a 0.7°C increase may seem insignificant, even a small increase represents an enormous amount of additional heat and related risks. Oceans play a principal role in climactic balance, covering 71% of the Earth’s surface, and protects us by absorbing more than 90% of the excess heat trapped by pollution. With increasing global heat & CO2 levels, we are pushing the oceans to their limits, as new evidence suggests that with continued warming the ocean’s capacity to absorb more CO2 could stall and even reverse in the future. This means that ‘even a 0.7°C increase is a step too close to potential stalling or reversal. 

The Copernicus record follows six months of unusually warm oceans and reflects the combined effects of long-term human-driven warming and the early development of El Niño (a natural warming of the tropical Pacific Ocean that affects global weather patterns), which is expected to strengthen during the second half of 2026. Warmer oceans fuel stronger storms, heavier rainfall, rising sea levels, and widespread disruption to marine ecosystems. 

What is Happening? 

• June 2026 has become the warmest June on record & sea surface temperatures have remained 0.35–0.73°C above the long-term average over the past three years. 
• By the end of June 2026, around 82% of the global ocean was experiencing marine heatwave conditions, the second-largest extent ever recorded, just behind 2024 (83%). 
• The World Meteorological Organization (WMO) declared the onset of El Niño on 2 June 2026, and NOAA confirmed its development on 11 June. Forecasts indicate El Niño is likely to strengthen during the second half of 2026, increasing the likelihood of further ocean and atmospheric temperature records.  
• Parts of the North Pacific, equatorial Pacific, and North Atlantic recorded sea surface temperatures more than 1.5°C above average, placing increasing stress on marine ecosystems and coastal communities. 

Why This Keeps Getting Worse: The Overheating Planet and Polar Change 

Human-caused carbon pollution is trapping more heat in the atmosphere, and over 90% of that excess heat is absorbed by the ocean. As the ocean absorbs and stores more heat, rising sea surface temperatures contribute to more frequent and intense marine heatwaves, can strengthen storms, , increase evaporation, and raise the risk of heavier rainfall, flooding, and sea-level rise. Warmer ocean conditions can also influence climate patterns such as El Niño (a natural warming of the tropical Pacific Ocean that affects global weather patterns). Research shows that continued deep ocean warming could shift El Niño patterns eastward and increase the frequency of extreme El Niño events by 40–80% compared with the current climate, potentially amplifying associated impacts such as extreme heat and rainfall. 

Beyond the Ocean: How Hotter Seas Increase Risks Globally 

• Stronger storms and flooding: Warmer oceans provide more heat and moisture to the atmosphere, increasing the potential for more intense tropical cyclones, heavier rainfall, and coastal flooding. 
• Sea-level rise: Ocean warming causes seawater to expand while accelerating the melting of land-based ice, increasing the risk of coastal erosion, flooding, and damage to homes and infrastructure. 
• Marine ecosystems and food security: Marine heatwaves disrupt coral reefs, fisheries, and marine food webs, threatening seafood supplies, coastal livelihoods, and biodiversity. 
• Public health: Warmer oceans can increase the risk of harmful algal blooms, reduce seafood availability, damage livelihoods in coastal communities, and contribute to more severe weather events that threaten lives and health. 

Urgent Response Needed 

What Needs To Change? 

• Strengthen coastal resilience through better flood protection, restoring natural coastal barriers (such as mangroves and wetlands), and building climate-resilient infrastructure.  
• Expand ocean monitoring and early warning systems to improve forecasts of marine heatwaves, storms, and coastal flooding.
• Protect and restore marine ecosystems (such as coral reefs, mangroves, salt marshes, and seagrass meadows) that support fisheries, store carbon, and help reduce coastal flooding.  

 What YOU Can Do: 

• Protect and restore marine ecosystems through supporting organizations like the Coral Reef Alliance, United Nations Environment Programme (Regional Seas Programme),  Intergovernmental Oceanographic Commission, UN Oceans & Agriculture Organization of the United Nations (Fisheries and Aquaculture Division).
• Follow evacuation and emergency guidance during storms, coastal flooding, and extreme weather events. Check on elderly and disabled neighbours. 
• Support the protection of coastal habitats such as wetlands, mangroves, and seagrass meadows that help reduce flooding and protect marine life.  
• Support community initiatives and be mindful of choices within your control, such as using public transport, cycling, or electric vehicles if possible, switching your heating to renewable energy, and volunteering at local projects or green spaces that reduce carbon pollution driving the overheating planet. 
• Stay informed about marine heatwaves, coastal flooding, and severe weather warnings issued by national meteorological agencies. 

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Read more: Sea Level Rise | Health risks | Climate Risks Daily 

Original source:June 2026: Global Ocean Temperatures Reach New Record | CMEMS