Open ocean — mean ocean temperature

Page Last modified 19 Nov 2021
2 min read
The planet’s oceans are warming, and that has many implications. Changes in ocean temperature can have widespread effects on marine species and biodiversity, with direct and indirect impacts on both natural and human activities, from ecosystem services to the fishing industry. Higher ocean surface temperatures can increase water vapour in the atmosphere, which influences weather both at sea and over land. Ocean warming in coastal areas can trigger algal blooms and bacterial outbreaks, which can be dangerous to marine life, human health and industries relying on tourism, fisheries, etc.

Key messages

  • Annual mean sea surface temperature has increased in all European regional seas. Further ocean warming is expected in future, potentially exceeding 3 °C by the end of this century under a high-emissions scenario, with somewhat lower warming for the Atlantic than for the other regional seas.

Sea surface temperature


Sea surface temperature (SST) is a key indicator of climate change in the ocean. SST represents the temperature of sea water at or near the surface over different timescales (e.g. seasonally and annually).

Note that different methods have been used historically to measure SST (ships, buoys and satellites), which requires careful consideration when building homogeneous data sets.

Index factsheet (ETC/CCA Technical Paper): Sea surface temperature


The index is easy to interpret and provides information for a variety of applications, mostly related to marine ecosystems and fisheries. Increasing SSTs in coastal areas can trigger algal blooms and outbreaks of vibrio bacteria, which can negatively affect human health and recreation.

Past and projected changes

Annual mean SST has increased in all European regional seas since 1870, particularly since the late 1970s.

Further increases are projected in the future, and these could exceed 3 °C by the end of the 21st century under the high-emissions scenario (representative concentration pathway (RCP)8.5). The greatest increases are projected for the Arctic Ocean, the North Sea and the Mediterranean Sea, whereas smaller SST increases are projected for the Atlantic Ocean.

Further information (EEA indicator assessment): European sea surface temperature 

Annual mean sea surface temperature for European seas

Sea Surface temperature


Notes:   The black line shows the annual values for 1979-2018 from reanalysis data, and the dashed horizontal line shows the mean for 1986-2005. Solid grey, blue, yellow and red lines represent the ensemble median of model simulations for the historical period and under low-, medium- and high-emissions scenarios (RCP2.6, RCP4.5 and RCP8.5, respectively) (smoothed by a 20-year moving average). Shaded areas show the 15th and 85th percentile ranges of the model ensemble. The size of the model ensemble used for each scenario is shown by the coloured numbers in the top-right corner. European seas include all sea surfaces within 25 °W-50 °E and 34 °N-75 °N.

Source:  ERA5 and bias-adjusted CMIP5 data. 

Projected changes in annual mean sea surface temperature in European seas under the high-emissions scenario (RCP8.5)

Notes:   The top panel shows the 1986-2005 mean values based on the reanalysis. The central row shows the 15th and 85th percentiles of projected values for near and far future. The projected changes compared with the 1986-2005 reference period are reported on the bottom row.

Source:  ERA5 and bias-adjusted CMIP5 data.

Chapters of the Europe's changing climate hazards report

  1. Heat and cold

  2. Wet and dry

  3. Wind

  4. Snow and ice

  5. Coastal

  6. Open ocean


Back to main page of the report


Geographic coverage



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