1.7 Coastal sea-surface temperature

• Sea-surface temperatures around the UK coast have risen over the past three decades by about 0.7ºC. 

Long observational data sets of the temperature of the coastal sea are available from a few point locations around the UK (see references to useful websites at the end of this paragraph). However, a more representative picture of trends can be gathered by using global gridded data sets of sea-surface temperature (SST, typical of the first few metres below the sea surface) and selecting all the grid squares which border the UK coastline. This is done in Figure 1.15, using a global data set of observations (Rayner et al. 2003). Also shown in this figure are the decadal variations and trends over a similar area in the night marine air temperature (NMAT, Rayner et al. (2003)), the air temperature measured over sea at night when it is unaffected by possible errors due to solar radiation. These show good agreement over the last century with the SST and hence act to corroborate the latter. Despite considerable year-to-year and even decade-to-decade variability, a clear coastal SST increase of about 0.7ºC over the past three decades is evident. Comparison with Figure 1.4 shows that coastal SST has warmed more slowly than CET, partly because SST temperatures generally lag behind air temperatures over land, but also because of a much smaller warming off northern Scotland, possibly due to local natural variability.