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Indicator Assessment
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.4.0.0.0, ERSSTv5 and HadISST).
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].
Projections
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.4.0.0.0 Data Set’,Journal of Geophysical Research: Atmospheres 124, no. 14 (27 July 2019): 7719–63, https://doi.org/10.1029/2018JD029867.
[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, https://doi.org/10.1029/2002JD002670.
[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, https://doi.org/10.1175/JCLI-D-16-0836.1.
[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, https://doi.org/10.1038/s41597-019-0236-x.
[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, https://doi.org/10.1016/j.rse.2010.10.017.
[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, https://doi.org/10.1038/s41467-018-03732-9.
[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, https://doi.org/10.1111/gcb.12662; 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, https://doi.org/10.1038/s41558-019-0412-1.
[viii] Craig Baker-Austin et al., ‘Heatwave-Associated Vibriosis, Sweden and Finland, 2014’,Emerging Infectious Diseases 22, no. 7 (2016): 1216–20, https://doi.org/10.32032/eid2207.151996; 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, https://doi.org/10.1073/pnas.1609157113.
[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), https://www.ipcc.ch/srocc/download-report/.
[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), https://www.ipcc.ch/srocc/download-report/, 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, https://doi.org/10.1007/s00382-019-04661-z.
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.
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.
Not applicable.
Not applicable.
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.
No uncertainty has been specified
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/sea-surface-temperature-3/assessment or scan the QR code.
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