This indicator monitors trends in average SST anomalies in Europe’s regional seas and in the global ocean. Care must be taken when comparing the results reported here with previous versions of the indicator, as differences can arise from the choice of underlying data sets.
SST is an important physical characteristic of the oceans. It varies naturally with latitude, being warmest at the equator and coldest in the Arctic and Antarctic regions. As the oceans absorb more heat, SST will increase (and heat will be redistributed to deeper water layers). Increases in the mean SST are also accompanied by increases in the frequency and intensity of marine heatwaves (that is, when the daily SST exceeds a locally and seasonally defined threshold).
Increases in SST can lead to an increase in atmospheric water vapour over the oceans, influencing entire weather systems. The North Atlantic Ocean plays a key role in the regulation of climate over the European continent by transporting heat northwards and redistributing energy from the atmosphere to the deep parts of the ocean. The Gulf Stream and its extensions, the North Atlantic Current and Drift, partly determine weather patterns over the European continent, including precipitation and wind regimes. One of the most visible physical ramifications of increased temperature in the oceans is a reduction in the area of sea ice coverage in the Arctic polar region.
Temperature is a determining factor for the metabolism of species, and thus for their distribution and phenology, such as the timing of seasonal migrations, spawning events and peak abundances (e.g. plankton bloom events). There is an accumulating body of evidence suggesting that many marine species and habitats, such as cetaceans in the North Atlantic Ocean, are highly sensitive to changes in SST. Increased temperature may also increase stratification of the water column. Such changes can significantly reduce vertical nutrient fluxes in the water column, thereby negatively influencing primary production and phytoplankton community structure. Further changes in SST could have widespread effects on marine species and cause the reconfiguration of marine ecosystems .
Methodology for indicator calculation
This indicator primarily uses information from the HadISST1, HadSST4, Extended Reconstruction Sea Surface Temperature version 5 (ERSSTv5), European Space Agency Sea Surface Temperature Climate Change Initiative (ESA SST CCI) Analysis and Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) 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 data set or other data sets. These lakes were masked out of the OSTIA data set.
There is a small, geographically varying difference 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 0.2m; 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 was assessed as the range of the three data sets — HadISST1, ERSSTv5 and HadSST4 — 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 paper by Kennedy et al.. Correlated errors were assumed to have been correlated within a year and uncorrelated between years.
Methodology for gap filling
In February 2021, the European Commission adopted a new EU strategy for adaptation to climate change . The new strategy sets out how the European Union can adapt to the unavoidable impacts of climate change and become climate resilient by 2050. It has four principle objectives: to make adaptation smarter, swifter and more systemic, and to step up international action on adaptation to climate change. The strategy builds on the 2018 evaluation of the 2013 EU adaptation strategy accompanied by a Commission staff working document . An open public consultation was conducted in preparation for the new strategy between May and August 2020.
No targets have been specified.
Data sets uncertainty
Systematic observations of SST began around 1850. More recently, manual measurements have been complemented by satellite-based observations that have a high degree of temporal resolution and wide geographical coverage, and by measurements from drifting buoys and Argo floats that automatically measure temperature and salinity below the ocean surface.
No uncertainty has been specified.