Marine heatwaves continue to intensify and expand, with June 2025 breaking records for sea surface temperatures and heatwave extent across Europe and the global ocean. Intense heatwaves are impacting 62% of the Mediterranean. While some regions show signs of easing, others remain under severe thermal stress.
Key Highlights
- In the Mediterranean Sea, June 2025 was the warmest June on record with a mean surface temperature (SST) of 23.86 ± 0.47°C
- 62% of the Mediterranean Sea surface was affected by marine heatwaves of categories strong or higher in June 2025 – the highest extent ever recorded.
- 72% of the global ocean surface recorded above-average temperatures, with 20% experiencing marine heatwaves on 30 June 2025.
- Marine heatwaves are increasing in frequency and severity, threatening marine ecosystems and coastal communities worldwide.
Overview of June and the first half of 2025
Global Ocean
- June 2025 was the third warmest June on record globally after 2023 and 2024, with a mean sea surface temperature (SST) of 20.75 ± 0.07°C. 9 of the hottest months of June have occurred during the last 10 years.
- 72% of the global ocean surface recorded SST above the long-term average (using the reference period 1993-2022).
- 20% of the global ocean was affected by high intensity marine heatwaves (category strong or above) at the end of June.
- Global SST for the first half of 2025 with 20.89 ± 0.06°C was the second warmest on record after 2024 (21.04 ± 0.06°C).
Mediterranean Sea
- June 2025 was the warmest June ever recorded, with a mean SST of 23.86 ± 0.47°C—surpassing the previous high of 2003.
- 88% of the basin experienced above-average temperatures this month; more than 60% of the area saw monthly mean SSTs at least +1°C above normal, and nearly 30% exceeded +2°C.
- The western Mediterranean was the hardest hit, with marine heatwaves reaching record levels for intensity, duration, and extent.
- At the peak, 62% of the Mediterranean Sea surface was affected by a high intensity marine heatwave (category high or above), compared to 40% for the same period last year.
- The first half of 2025 (January–June) was the warmest on record, with 88% of the basin having been exposed to high intensity marine heatwave conditions during this period.
North Atlantic Ocean
- June 2025 was the third warmest June on record, with a mean sea surface temperature (SST) of 22.84 ± 0.20°C.
- 71% of the region recorded above-average SSTs, with the most pronounced anomalies observed along the European and North American coastlines.
- The first half of 2025 was also the third warmest on record, with 50% of the North Atlantic affected by high intensity marine heatwave conditions during this period.
Weekly forecasts: 5-12 July 2025
Mediterranean Sea
- Western basin: marine heatwave intensity and area are decreasing, shifting from strong/severe to moderate/locally strong.
- Eastern basin: heatwave also diminishing, with only a few moderate areas remaining.
North Atlantic Ocean
- Heatwave shrinking off Portugal but expanding mid-basin; intensity remains strong/severe.
- North Sea heatwave decreasing; moderate to locally extreme patches remain.
- From eastern Florida to the mid-Atlantic: shrinking near Florida, expanding in the mid-basin; intensity stable (moderate to severe).