Ocean Temperature Bulletin
January 2026

Mercator Ocean International (MOi) oceanographers examine marine heatwaves across the global ocean. They analyse a variety of datasets from observation analyses
(satellite sea surface temperature maps) to model analyses
(assimilating satellite and in situ observations) and model forecasts.¹

All images in this article can be used freely and should be credited with the following information :

Image source: European Union, Copernicus Marine Service Data 2025 © Mercator Ocean .

Key takeaway

January 2026 was the 4th warmest January on record for the global ocean (between 60°S and 60°N) with a mean sea surface etmperature (SST) of 20.73 ± 0.06°C.
In the European regional seas – the Mediterranean Sea and the North Atlantic (bewteen 0°N and 60°N) -January 2026 also ranked the 4th warmest with mean SSTs reaching 17.05 ± 0.10°C and 20.87 ± 0.06°C respectively.
Record sea surface temperatures were registered around the global ocean for a January month. In the Mediterranean Sea, most of the basin ranked within the 10 warmest years. Several regions of the North and South Pacific and in the Southern Ocean, recorded their warmest or 2nd warmest January this year.
Marine heatwave events in the North Atlantic were the 3rd longest ever recorded for a January month (behind 2025 and 2024).

sea Surface Temperature

January 2026, at global level (between 60°S and 60°N), was the 4^th warmest January on record, with a mean Sea Surface Temperature (SST) of 20.73 ± 0.06°C — behind 2016 ( 20.80 ± 0.15 °C), 2025 (20.84 ± 0.06 °C) and 2024 ( 21.03 ± 0.06 °C ).
In the Mediterranean Sea, January 2026 SST was the 4^th warmest January of the past 33 years, with a mean SST of 17.05 ± 0.10°C, ranking behind 2025 (17.07 ± 0.09°C), 2024 (17.17 ± 0.16°C) and 2023 (17.25 ± 0.11 °C).
In the North Atlantic (between 0°N and 60°N), January 2026 was also the 4^th warmest January month with a mean SST of 20.87 ± 0.06°C. The record of 2024 reached 21.19 ± 0.05°C.

Sea surface temperature anomalies

January 2026 Mean SST Anomaly relative to a 30-year climatology (1993-2022), calculated using daily data from Mercator Ocean International’s GLO12 analysis and forecasting system for 2025 and from the GLORYS12 reanalysis for the climatological mean.

January 2026 mean SSTs are above average for 69% of the global ocean (between 60°S and 60°N), with 12% exceeding the average by at least 1°C.

Almost the entire Mediterranean Sea (95%) showed above-average SSTs, with 37% of the basin reaching at least 1°C above average, mainly in the eastern part.
The North Pacific Ocean showed widespread high SSTs at midlatitude spanning the entire width of the basin and reaching 3°C above average in the western part. Above-average SSTs were also observed in the western South Pacific, particularly northeast of New Zealand, exceeding 2°C. Off the coast of Chile, SSTs reached more than 2°C above average. The equatorial region is characterized by SSTs well below average, locally reaching -2°C. This marks the current La Niña phase of ENSO.
The North Atlantic recorded above-average SSTs over 72% of its area (between 0°N and 60°N), mainly in the subtropical part of the basin, with anomalies reaching 1.5-2°C. Northeastern Europe is also experiencing anomalies exceeding 1°C locally. In the South Atlantic, between 15°S and 45°S, SSTs exceeded 2°C above average, mainly off the coast of South Africa.
Widespread above average SSTs are observed in the Southern Ocean, between 30°W and 120°E, reaching up to 1.5-2°C locally.

Rankings of January 2026 mean sea surface temperature since 1993. Blank areas mean that January 2026 mean SST doesn’t rank in the 10 warmest or 10 coolest mean SST since 1993. Data: GLO12 (daily SST 2021-20206), GLORYS12 (climatology 1993-2020) Blank areas mean that January 2026 mean SST doesn’t rank in the 10 warmest or 10 coolest mean SST since 1993. Credit: EU. Copernicus Marine Service/Mercator Ocean.

Most of the Mediterranean was occupied by average SSTs among the 10 warmest years. More scattered, these SSTs were the warmest or second warmest recorded for a month of January.
In the North Atlantic, SSTs reached record levels in northern Europe and in the subtropical region, from the Caribbean to the middle of the basin.
In the South Pacific, between 15°S and 45°S, temperatures reached in the eastern part of the basin make January 2026 the warmest January on record, or the second warmest.
In the North Pacific, most of the basin is experiencing one of the ten warmest months of January on record. More patchily, January 2026 SSTs are approaching or reaching record levels, particularly between 30°N and 60°N, and off the coast of the Philippines. In the South Pacific, mainly northeast of New Zealand and off the coast of South America, January 2026 was among the two warmest months of January ever recorded.
The Southern Ocean also reached SST records for the month of January, particularly between 50°E and 100°E.

Ongoing Marine Heatwaves

Month of onset for the ongoing MHWs on the 31st January 2026. The colors indicate the month during which the MHW started. For instance, ocean pixels in red correspond to an MHW that developed during January 2026 and are less than one month old, in orange MHW between 1 and 2 months old, etc.

On 31^st of January, 18% of the global ocean (between 60°S and 60°N) was affected by MHWs.
The majority of these MHWs developed recently, with 13% of the global Ocean (between 60°S and 60°N) affected by MHWs less than 1 month old and more than 4% by events between 1- and 2-month-old.
The oldest MHWs are in the North Atlantic, particularly in the subtropical region and north of Europe, as well as in the Southern Ocean between 60°E and 90°E. On a more localized scale, the North Pacific also has regions of persistent MHWs.

Total Surface Marine Heatwaves

Global Ocean (between 60°S and 60°N)

In January 2026, the total surface area of MHW (black line) remained stable around 18% of the global ocean. The majority of MHWs events were moderate categories (~15% of the global ocean) and, to a lesser extent, strong categories (~2% of the global ocean).

North Atlantic (between 0°N and 60°N)

In the North Atlantic, the total surface area of MHW remained stable around 22%, with a slight decrease at the end of the month, falling below 21%.
These events consist mostly of moderate and strong categories (18-20% and 3%, respectively). For comparison, in January 2025, the total MHW extent varied between 42% and 36% of the North Atlantic, with the noteworthy presence of strong categories (7-10%) (not shown).

Mediterranean Sea

In the Mediterranean Sea, the total MHW surface decreased from 45% to 41% during the month of January 2026, with a drop below 35% in the middle of the month. These MHWs were mainly moderate in category, with around 3-4% of strong events.
For comparison, in 2025, the total surface area of MHW increased from 21% to 63% during the month of January (not shown).

Total Number Marine Heatwaves

Intense (strong, severe and extreme) marine heatwaves in January 2026

January 2026 MHW days of strong and higher category. Number of days during which a MHW of category strong, severe or extreme occurred in January 2026. Blank areas mean that no MHW of strong or higher category happened during the month. Blue shaded areas in the polar regions represent the sea ice maximum from the climatological period (1993-2022). Monitoring SST extremes with the MHW categorization approach as used here is not best suited for such regions.

9% of the surface of the global ocean was impacted by strong-or-higher MHW conditions for at least 1 day during January 2026.
This is the 5^th widest extent of the last 33 years, after 2020, 2016, 2025 and 2024 (31%).
The South Pacific off the coast of Chile and the Southern Ocean between 50°E and 90°E were strongly affected, with MHWs lasting the entire month.

Year by year evolution of the surface impacted by strong and higher MHW during months of January. The size of the bar represents the proportion of the global ocean (between 60°S and 60°N) exposed to a strong or higher MHW during the month. As indicated by the colours, the proportion exposed to such MHWs is categorized according to the number of days impacted during the month.

10% of the North Atlantic (between 0°N and 60°N) was impacted by strong, or higher, MHW conditions for at least 1 day.
This corresponds to the 4^th largest extent for a January month – behind 2020 (11%), 2025 (24%) and 2024 (44%). Worth noting, 4% of the region was affected by intense MHW conditions (Strong or higher) for more than 10 days, mainly in the subtropical part of the basin and north of Great Britain.

15% of the Mediterranean Sea was affected by strong-or-higher MHW conditions for at least 1 day, which is the 5^th largest extent for a January month, after 2011 (16%), 2025 (27%), 2023 (42%) and 2024 (42%).

Statistics

Marine heatwave average duration, intensity, occupied surface and activity in January 2026

MHW Characteristics for January months from 1993 to 2026. Duration, intensity, extent and activity averaged for each January month between 1993 and 2026 for the global ocean (left), for the Mediterranean Sea (center) and the North Atlantic Ocean (right). January 2026 is highlighted with a blue edge.

January 2026 was the 5^th most extreme January month in terms of MHW intensity for the global ocean, after 2016, 2025, 2024, 1998. It was also the 6^th January month with longest MHW events on average after 2023, 2016, 2025, 2024 and 1998.
In the Mediterranean Sea, January 2026 was the 5^th most extreme January on average but not as intense and long as January 2011 or 2014, and far from the most extreme episode in January 2023.
In the North Atlantic, January 2026 was the 3rd most extreme January in terms of MHW duration, and the 4^th in intensity, far from January 2024 events.

About the Bulletin

Mercator Ocean International 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).

Data sets 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. U. Copernicus Marine Service Information (CMEMS). 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 (CMEMS). 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 (CMEMS). 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 (CMEMS). 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 November 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. 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. 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 previous March (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

Ocean Temperature BulletinJanuary 2026