A monthly reporting on mean sea surface temperatures and marine heatwave conditions.
Key takeaways
In Europe
- June 2025 was the warmest June on record for the Mediterranean Sea, with mean temperatures of 23.86 ± 0.47°C.
- 88% of the Mediterranean Sea recorded sea surface temperatures above average – with more than 60% at + 1°C, and almost 30% at +2°C.
- The western part of the Mediterranean Sea is the most impacted by these high anomalies.
- Marine heatwaves in the Mediterranean Sea were the most extreme in intensity, duration and extent.
- 62% of the total surface of the Mediterranean Sea was touched by an intense marine heatwave – a marine heatwave of strong or higher category; the highest ever recorded in the basin.
- June 2025 was the 3rd warmest June for the North Atlantic region, with mean temperatures of 22.84 ± 0.20 °C.
Globally
- Mean sea surface temperatures reached 20.75 ± 0.07 °C – the 3rd warmest June for the ocean globally.
- 72% of the global ocean recorded mean sea surface temperatures above average.
- June 2025 was the 3rd most intense June on record for marine heatwaves globally.
SEA SURFACE TEMPERATURE
Figure 1: Daily sea surface temperatures averaged for the global ocean (top), the Mediterranean Sea (left) and the North Atlantic Ocean (right) between 1991-2020 using ESA’s Climate Change Initiative (grey shades), and between 2021-2025 (colored shades) using Mercator Ocean International’s GLO12 analysis and forecast.
- In the global ocean, between 60°S and 60°N, June 2025 was the 3rd warmest June on record (after 2023 and 2024), with a mean Sea Surface Temperature (SST) of 20.75 ± 0.07 °C.
- For the Mediterranean Sea, June 2025 was the warmest June on records with a mean SST of 23.86 ± 0.47°C, breaking 2022 record of 23.72 ± 0.36°C.
- For the North Atlantic, June 2025 was the 3rd warmest June month (after 2023 and 2024) with a mean SST of 22.84 ± 0.20 °C.
Sea surface temperature anomalies
- June 2025 mean sea surface temperature are above average (see figure 2) for 72% of the global ocean (between 60°S and 60°N), with 12% exceeding the average by at least 1°C.
- 88% of the Mediterranean Sea showed monthly mean SSTs that were above average for a typical June, with more than 60% exceeding the average by at least 1°C (and almost 30% by at least 2°C). The western part is the most impacted by these high anomalies.
- The Pacific Ocean shows high SSTs at midlatitude in both hemispheres, with a large region with SSTs reaching 3°C above average in the northern part.
- In the North Atlantic, SSTs are predominantly above average (covering 71% of the area) with the highest anomalies observed on the eastern side along the European coast and on the western side along the North American coast (reaching more than 1.5°C above average).
- The same is observed for SSTs in the Indian Ocean with above average SST reaching almost 2°C locally between Australia and Madagascar.
Note: In the central Pacific, along the equator, we still observe below-average SSTs (reaching -1°C).
MARINE HEATWAVES
Marine heatwaves (MHWs) are extreme rises in ocean temperature for an extended period of time. They can occur at different locations in the ocean, and their magnitude and frequency have increased over the last couple of decades, with harmful impacts on ecosystems, and human activities.
Ongoing marine heatwaves: 30 June 2025
Long warming events may induce important stress on marine life. Here is represented the ongoing marine heatwave (MHW) events on 30 June and their onset time.
- 20% of the global ocean (between 60°S and 60°N) was affected by MHWs on the 30th of June.
- The majority of these MHWs developed recently, with 16% of the global Ocean (between 60°S and 60°N) affected by MHWs less than 1 month old andmore than 3% by events between 1- and 2-month-old.
months old, etc.
Total surface exposed to marine heatwaves: July 2024 – June 2025
We monitor daily the surface occupied by MHWs and show for the past year (since July 2024) the proportion of the global Ocean (between 60°S and 60°N) exposed to MHWs. We focus on the evolution over the past June 2025 (grey bar).
Global Ocean
- In June the total surface of MHW (black line) ranges between 18% to 19.5% over 60°S and 60°N.
- These MHWs consist mainly of moderate and strong events (16% and 3%, respectively, by the end of the month).
- For comparison, in June 2024, MHW total extent varied between 30% and 35% of the global ocean (between 60°S and 60°N), with almost 10% of strong category (not shown).
Mediterranean Sea
In the Mediterranean Sea :
- For the Mediterranean Sea, the total MHW surface showed a rapid increase from ~15% to 55% by the end of June, with a peak of 64% mid-June. These events consist mostly of moderate and strong categories (33% and 21% by the end of the month, respectively).
- We observe a peak of moderate category of 50% in the first half of June, while the strong category peaks during the second half of the month, to 29%.
- For comparison, in June 2024, the total MHW extent remained below 40% of the Mediterranean Sea, with mostly moderate, strong and severe categories (not shown).
North Atlantic
Figure 6: Surface occupied by MHWs in the North Atlantic (between 0°N and 60°N) between July 2024 and June 2025 based on daily monitoring. The black solid line represents the total surface of MHW, while the colored lines represent the surface of each MHW category. The gray background highlights the month of June 2025.
For the North Atlantic between 0°N and 60°N:
- For the North Atlantic (between 0°N and 60°N), the total MHW surface remains stable around 19% during the month of June 2025.
- These events consist mostly of moderate and strong categories, with a decrease of moderate and an increase of strong categories by the end of the month (11% and 6%, respectively).
- For comparison, in June 2024, the total MHW extent decreased from ~44% to ~39%, with moderate and strong categories (not shown).
Total number of marine heatwave days in June 2025
11% of the surface of the ocean was impacted by strong, or higher, MHW conditions for at least 1 day. The southeast Asia region and the European region of Western Europe are the most affected.
Figure 7: Total number of days during which a MHW of category strong, severe or extreme occurred in June 2025. Light green colour corresponds to areas where a total of 10 to 15 days of strong or higher MHW were observed during the month of June of 2025. Blank areas mean that no MHW of strong or higher category happened during the month.
Longer and more frequent MHWs increase heat stress on marine ecosystems, especially intense MHWs (i.e. MHWs of strong or higher category). Thus, we monitor the number of MHW days globally, to highlight the region(s) often impacted or impacted by long MHWs.
Marine heatwave June statistics
Figure 7: MHW characteristics for all June months between 1993 and 2025. Duration, intensity, extent and activity averaged for each June month between 1993 and 2025 for the global ocean (left), for the Mediterranean Sea (centre) and the North Atlantic Ocean (right). June 2025 is highlighted with a blue edge.
The MHW statistics (duration, intensity, surface occupied and activity) for June 2025 are compared to those for June months from previous years since 1993.
- On a global scale, June 2025 is the 3rd most extreme June month in terms of MHW intensity (after 2024 and 2023).
- In the Mediterranean Sea, June 2025 is the most extreme June month on records in terms of MHW.
- In the North Atlantic, June 2025 is the 5th most extreme June in terms of MHW.
About the bulletin
Mercator Ocean International (MOi) publishes a monthly sea surface temperature bulletin reporting on mean temperature and marine heatwave conditions for the month just passed. It includes:
- Regions where MHWs are present and the time these events started,
- Timeseries showing the total surface occupied by MHWs globally and for the European region,
- The total number of days of exposure to MHW during the month (including only strong and higher intensity categories).
Image citation: European Union, Copernicus Marine Service Data 2025 © Mercator Ocean
All images in this article can be used freely and should be cited with the information above.
Datasets and Products
Sea Surface Temperature
The results are obtained using the Copernicus Marine Service global analysis and forecasting system together with observation-based products.
- GLOBAL_ANALYSISFORECAST_PHY_001_024 Global Ocean Physics Analysis and Forecast sea surface temperature. E.U. Copernicus Marine Service Information. Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00016
- ESA SST CCI reprocessed sea surface temperature analyses. E.U. Copernicus Marine Service Information. Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00169
- NOAA OI SST V2 High Resolution Dataset data provided by the NOAA PSL, Boulder, Colorado, USA, from their website at https://psl.noaa.gov, Huang, B., C. Liu, V. Banzon, E. Freeman, G. Graham, B. Hankins, T. Smith, and H.-M. Zhang, 2021:
- Improvements of the Daily Optimum Interpolation Sea Surface Temperature (DOISST) Version 2.1, Journal of Climate, 34, 2923-2939. doi: 10.1175/JCLI-D-20-0166.1
- Global Ocean OSTIA Sea Surface Temperature and Sea Ice Analysis. E.U. Copernicus Marine Service Information. Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00165
- ODYSSEA Global Sea Surface Temperature Gridded Level 4 Daily Multi-Sensor Observations. E.U. Copernicus Marine Service Information. Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00016
Notes: The global analysis system was used to study the ocean surface temperature from 2021 and 2025. To study surface temperature for previous years (1991 to 2020), it was used the ESA CCI data. The other observation-based sea surface temperature products (OSTIA, OI SST and Odyssea) were used for calculating monthly mean and uncertainty values for the past month in 2025.
Marine Heatwaves
The results are obtained using the Copernicus Marine Service global systems including the analysis and forecasting system together with the reanalysis product.
- GLOBAL_ANALYSISFORECAST_PHY_001_024 Global Ocean Physics Analysis and Forecast sea surface temperature. E.U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00016
- GLOBAL_MULTIYEAR_PHY_001_030 Global Ocean Physics Reanalysis sea surface temperature. E.U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00021
Notes: The global analysis system was used to study MHWs for 2024 and 2025. To study MHWs for this month in previous years (1993 to 2023), it was used the reanalysis system. The reanalysis product was used for generating a daily climatology using the 30-year period from 1993 to 2022.
