Indicator Assessment

Sea surface temperature

Indicator Assessment
Prod-ID: IND-100-en
  Also known as: CSI 046 , CLIM 013
Published 04 Dec 2019 Last modified 30 Jun 2021
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  • All European seas have warmed considerably since 1870; the warming has been particularly rapid since the late 1970s.
  • The trend in sea surface temperature rise during the satellite era (since 1981), for which more comprehensive data are available, has been between around 0.2 °C per decade, in the North Atlantic, and 0.5 °C per decade, in the Black Sea.
  • Sea surface temperature is projected to continue to increase, depending on the emissions scenario, although more slowly than air temperature over land.
  • In parallel with the rise in sea surface temperature, the frequency and magnitude of marine heatwaves has increased significantly globally and in European seas. This rise is projected to continue rapidly, with increasing impacts on ecosystems and land climate.

Decadal average sea surface temperature anomaly in different European seas

Note: The figure shows decadal global and regionally averaged sea-surface temperature anomalies relative to a 1981-2010 baseline. The solid line shows a satellite-based series combining the SST CCI analysis (to 2016) with the OSTIA near-real time updates (to 2018). The shaded area in each plot indicates the upper and lower uncertainty range of the long-term evolution of the regional averages based on three global data sets (HadSST., ERSSTv5 and HadISST).

Data source:

Past trends

The production of consistent, long time series of sea surface temperature (SST) faces challenges owing to different measurement devices (in situmeasurements from ships and buoys, as well as remote measurements from satellites), associated different definitions (e.g. water depth and time of day of measurement), different bias correction methods, and different interpolation methods to account for incomplete spatial and temporal coverage. As a result, substantially different values for absolute SST and for SST trends may be reported for a particular ocean basin, depending on the underlying global or regional SST dataset. Despite those uncertainties, it is undisputed that SST has been increasing globally and in Europe during the last century.

The current indicator uses information from a range of SST data sets: HadSST4 [i], HadISST1.1 [ii] and ERSSTv5 [iii] cover a period reaching back to the mid-19th century whereas the ESA SST CCI version 2.1 [iv] and the OSTIA datasets [v] together cover the satellite era from 1981 to present only. The trends, although not necessarily the absolute SST levels, are consistent between the historical long-term data sets and the higher-resolution satellite-era data sets.

Figure 1 shows the SST development for the five European regional seas (coloured), in comparison to global SST (in black). All European seas have warmed considerably since 1870. For the Black Sea, consistent measurements begin in the 1950s, since which time it has clearly warmed. The warming has been particularly rapid since the late 1970s. The multi-decadal rate of SST rise during the satellite era (difference in decadal averages 1982-1991 to 2009-2018) has been between around 0.2 °C per decade in the North Atlantic and around 0.5 °C per decade in the Black Sea. Care must be taken when comparing the results reported here to previous versions of the indicator as differences can arise from the choice of underlying data sets.

In addition to changes in average SST, marine heatwaves are also increasing. Marine heatwaves (defined when the daily sea surface temperature exceeds a locally and seasonally defined threshold) have become more frequent globally and in European seas over the past century (1925 to 2016), leading to a considerable increase in marine heatwave days [vi]. These marine heatwaves have had considerable ecological impacts, including harmful algal blooms, with increased risks to human health, ecosystems and aquaculture [vii]. For example, recent marine heatwaves have led to unprecedented levels of vibriosis infections along the Baltic Sea and the North Sea coast [viii]. Marine heatwaves can also affect climate on land. For example, marine heatwaves in the Mediterranean Sea may have amplified heatwaves and heavy precipitation events over central Europe as well as triggered intense extratropical cyclones over the Mediterranean Sea [ix].


Globally averaged ocean temperatures at the surface and for different ocean depths will further increase in the 21st century. Owing to the thermal inertia of the ocean, global mean SST is projected to increase about 30 % slower than global mean surface temperature [x]. Quantitative SST projections are available only for some regional seas in Europe. For the Baltic Sea, the increase in summer SST during the 21st century under medium to high emissions scenarios is projected to be about 2 °C in the southern parts and about 4 °C in the northern parts [xi].

Marine heatwaves are projected to further increase in frequency, duration, spatial extent and maximum intensity [xii]. A recent analysis projects that under a high emissions scenario (RCP8.5), the Mediterranean Sea will experience at least one long lasting marine heatwave every year by the end of the 21st century, up to three months longer, about 4 times more intense and 42 times more severe than present-day events; the increase would be less strong under lower emissions scenarios [xiii].

[i] J. J. Kennedy et al., ‘An Ensemble Data Set of Sea Surface Temperature Change From 1850: The Met Office Hadley Centre HadSST. Data Set’,Journal of Geophysical Research: Atmospheres 124, no. 14 (27 July 2019): 7719–63,

[ii] N. A. Rayner, ‘Global Analyses of Sea Surface Temperature, Sea Ice, and Night Marine Air Temperature since the Late Nineteenth Century’,Journal of Geophysical Research 108, no. D14 (2003): 4407,

[iii] Boyin Huang et al., ‘Extended Reconstructed Sea Surface Temperature, Version 5 (ERSSTv5): Upgrades, Validations, and Intercomparisons’,Journal of Climate 30, no. 20 (October 2017): 8179–8205,

[iv] Christopher J. Merchant et al., ‘Satellite-Based Time-Series of Sea-Surface Temperature since 1981 for Climate Applications’,Scientific Data 6, no. 1 (December 2019): 223,

[v] Craig J. Donlon et al., ‘The Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) System’,Remote Sensing of Environment 116 (January 2012): 140–58,

[vi] Eric C. J. Oliver et al., ‘Longer and More Frequent Marine Heatwaves over the Past Century’,Nature Communications 9, no. 1 (December 2018): 1324,

[vii] Patricia M. Glibert et al., ‘Vulnerability of Coastal Ecosystems to Changes in Harmful Algal Bloom Distribution in Response to Climate Change: Projections Based on Model Analysis’,Global Change Biology 20, no. 12 (1 December 2014): 3845–58,; Dan A. Smale et al., ‘Marine Heatwaves Threaten Global Biodiversity and the Provision of Ecosystem Services’,Nature Climate Change 9, no. 4 (April 2019): 306–12,

[viii] Craig Baker-Austin et al., ‘Heatwave-Associated Vibriosis, Sweden and Finland, 2014’,Emerging Infectious Diseases 22, no. 7 (2016): 1216–20,; Luigi Vezzulli et al., ‘Climate Influence on Vibrio and Associated Human Diseases during the Past Half-Century in the Coastal North Atlantic’,Proceedings of the National Academy of Sciences 113, no. 34 (23 August 2016): E5062–71,

[ix] M. Collins et al., ‘Chapter 6: Extremes, Abrupt Changes and Managing Risks’, inIPCC Special Report on the Ocean and Cryosphere in a Changing Climate, ed. H.-O. Pörtner et al. (Cambridge, UK: Cambridge University Press, 2019),

[x] IPCC,Special Report on the Ocean and Cryosphere in a Changing Climate, ed. H.-O. Pörtner et al. (Cambridge, UK: Cambridge University  Press, 2019),, SPM, Footnote 29.

[xi] HELCOM, ‘Climate Change in the Baltic Sea Area: HELCOM Thematic Assessment in 2013’, Baltic Sea Environment Proceedings (Helsinki: Helsinki Commission, 2013).

[xii] IPCC,Special Report on the Ocean and Cryosphere in a Changing Climate.

[xiii] Sofia Darmaraki et al., ‘Future Evolution of Marine Heatwaves in the Mediterranean Sea’,Climate Dynamics 53, no. 3–4 (August 2019): 1371–92,

Supporting information

Indicator definition

  • This indicator monitors trends in average SST anomalies in Europe’s regional seas and in the global ocean.


  • Temperature (°C).


Policy context and targets

Context description

In April 2013, the European Commission presented the EU adaptation strategy package. This package consists of the EU strategy on adaptation to climate change (COM/2013/216 final) and a number of supporting documents. The overall aim of the EU adaptation strategy is to contribute to a more climate-resilient Europe.

One of the objectives of the EU adaptation strategy is to allow 'Better informed decision-making', which will be achieved by bridging knowledge gaps and further developing the European climate adaptation platform (Climate-ADAPT) as the ‘one-stop shop’ for climate adaptation information in Europe. Climate-ADAPT has been developed jointly by the European Commission and the European Environment Agency (EEA) to share knowledge on (1) observed and projected climate change and its impacts on environmental and social systems and on human health, (2) relevant research, (3) EU, transnational, national and subnational adaptation strategies and plans, and (4) adaptation case studies.

Further objectives include 'Promoting adaptation in key vulnerable sectors through climate-proofing EU sector policies' and 'Promoting action by Member States'. Most EU Member States have already adopted national adaptation strategies and many also have prepared action plans on climate change adaptation. The European Commission also supports adaptation in cities through the Covenant of Mayors for Climate & Energy initiative.

In September 2016, the European Commission presented an indicative roadmap for the evaluation of the EU adaptation strategy by 2018.

In November 2013, the European Parliament and the Council of the European Union adopted the EU's Seventh Environment Action Programme (7th EAP) to 2020, ‘Living well, within the limits of our planet’. The 7th EAP is intended to help guide EU action on the environment and climate change up to and beyond 2020. It highlights that ‘Action to mitigate and adapt to climate change will increase the resilience of the Union’s economy and society, while stimulating innovation and protecting the Union’s natural resources.’ Consequently, several priority objectives of the 7th EAP refer to climate change adaptation.


No targets have been specified.

Related policy documents

  • 7th Environment Action Programme
    DECISION No 1386/2013/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 20 November 2013 on a General Union Environment Action Programme to 2020 ‘Living well, within the limits of our planet’. In November 2013, the European Parliament and the European Council adopted the 7 th EU Environment Action Programme to 2020 ‘Living well, within the limits of our planet’. This programme is intended to help guide EU action on the environment and climate change up to and beyond 2020 based on the following vision: ‘In 2050, we live well, within the planet’s ecological limits. Our prosperity and healthy environment stem from an innovative, circular economy where nothing is wasted and where natural resources are managed sustainably, and biodiversity is protected, valued and restored in ways that enhance our society’s resilience. Our low-carbon growth has long been decoupled from resource use, setting the pace for a safe and sustainable global society.’
  • Climate-ADAPT: Adaptation in EU policy sectors
    Overview of EU sector policies in which mainstreaming of adaptation to climate change is ongoing or explored
  • Climate-ADAPT: Country profiles
    Overview of activities of EEA member countries in preparing, developing and implementing adaptation strategies
  • DG CLIMA: Adaptation to climate change
    Adaptation means anticipating the adverse effects of climate change and taking appropriate action to prevent or minimise the damage they can cause, or taking advantage of opportunities that may arise. It has been shown that well planned, early adaptation action saves money and lives in the future. This web portal provides information on all adaptation activities of the European Commission.
  • EU Adaptation Strategy Package
    In April 2013, the European Commission adopted an EU strategy on adaptation to climate change, which has been welcomed by the EU Member States. The strategy aims to make Europe more climate-resilient. By taking a coherent approach and providing for improved coordination, it enhances the preparedness and capacity of all governance levels to respond to the impacts of climate change.
  • Evaluation of the EU Adaptation Strategy Package
    In November 2018, the EC published an evaluation of the EU Adaptation Strategy. The evaluation package comprises a Report on the implementation of the EU Strategy on adaptation to climate change (COM(2018)738), the Evaluation of the EU Strategy on adaptation to climate change (SWD(2018)461), and the Adaptation preparedness scoreboard Country fiches (SWD(2018)460). The evaluation found that the EU Adaptation Strategy has been a reference point to prepare Europe for the climate impacts to come, at all levels. It emphasized that EU policy must seek to create synergies between climate change adaptation, disaster risk reduction efforts and sustainable development to avoid future damage and provide for long-term economic and social welfare in Europe and in partner countries. The evaluation also suggests areas where more work needs to be done to prepare vulnerable regions and sectors.


Methodology for indicator calculation

The current indicator primarily uses information from the HadISST1 (Rayner et al., 2003), HadSST4 (Kennedy et al., 2019), ERSSTv5 (Huang et al., 2017), ESA SST CCI Analysis (Merchant et al., 2019) and the OSTIA (Stark et al., 2007) data sets.

Each data set was averaged on to a common 5° latitude by 5° longitude monthly grid. These averaged data sets were used to calculate the regional area averages. Regional area averages were calculated by a weighted average of grid cell values where the weights were equal to the area of ocean in that grid cell (determined using the SST CCI analysis land mask). The OSTIA real-time updates include some lakes not considered in the SST CCI Analysis and other data sets. These lakes were masked out of the OSTIA analysis.

There is a small, geographically varying offset between the OSTIA and SST CCI Analysis data sets. The OSTIA data set represents the 'foundation' SST and the SST CCI Analysis data set represents SST at a depth of 0.2 m; at least part of the variability is due to these differences in definitions.

A monthly time series was calculated for each of the seas and regions. A trailing 120-month (i.e. decadal) mean was calculated from the monthly series. Consequently, the first available decadal mean for a series is 120 months after the start date of that series.

Uncertainty in the long-term data sets is assessed as the range of the three data sets (HadISST1, Rayner et al., 2003; ERSSTv5, Huang et al., 2017; and HadSST4, Kennedy et al., 2019), including the estimated uncertainty range from HadSST4. This therefore covers uncertainties arising from measurement, sampling, bias adjustment and spatial infilling, as well as structural uncertainty. The HadSST4 uncertainty range was calculated as described in the HadSST4 paper (Kennedy et al., 2019). Correlated errors were assumed to be correlated within a year and uncorrelated between years.

Methodology for gap filling

Not applicable.

Methodology references



Methodology uncertainty

Not applicable.

Data sets uncertainty

Systematic observations of SST began around 1850. More recently, these manual measurements have been complemented by satellite-based observations that have a high resolution in terms of time and a wide geographical coverage, as well as by measurements from drifting buoys and Argo floats that automatically measure temperature and salinity below the ocean surface.

Rationale uncertainty

No uncertainty has been specified

Data sources

Other info

DPSIR: Impact
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
Indicator codes
  • CSI 046
  • CLIM 013
Frequency of updates
Updates are scheduled every 2 years
EEA Contact Info


Geographic coverage

Temporal coverage



Filed under:
Filed under: water temperature
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