Oceanic Warming

As the earth is warmed by increasing atmospheric greenhouse gases, the vast majority (91%) of this excess heat is taken up by the oceans (Lindsey and Dahlman, 2023). 2024 was a record year for Sea Surface Temperatures*, averaging ~21°C throughout January to April (BBC, 2024). While the tail end of the 2023 El Niño event did contribute to this extreme heat, the underlying trend of heating oceans is undeniably driven by increasing greenhouse gases. 71% of the world's coastlines warmed over the period of 1982–2010 (Ruela et al 2020), while global SSTs have consistently measured above the 1955-2006 average since 1994 (Lindsey and Dahlman, 2023), as shown in figure 1. 

A few areas of the global ocean have not followed this warming trend, instead cooling at the surface as shown in fig. 2. Notably, a large cooling area is found around the Northern Atlantic and the Labrador Sea, to the West of the UK (Garcia-Soto et al, 2021). With another area of cooling located around the West Antarctic, the melting of glacial ice is likely contributing to these cooling surface waters. 

Of the warming oceans, the seas to the North of Europe (e.g. the Norwegian and Barnet seas) are projected to experience the most intense warming globally, as is demonstrated in fig. 3. Both moderate and extreme emissions scenarios display a cluster of warming around Northern Europe, potentially being felt as far west as the UK under the extreme scenario (Ruela et al, 2020).

*SST is a common metric for monitoring ocean temperatures, as the sea surface is the first layer of the ocean to reflect warming trends. 

Scotland’s Temperatures:

Fig. 4 demonstrates the current condition of Scotland’s waters, representing SST on the longest and shortest days of 2024, as well as on the  hottest ever recorded day (Cefas Eutrophication xcube Viewer, 2024). The East Grampian coastline is revealed to be one of the country’s coldest coasts, along with the Highlands and Islands. Even on the extremely hot 19th Jul (Met Office, 2024), temperatures on the East Grampian coast sat at only ~12 -15°C. 

As discussed, much variation exists in the waters connected to Scotland’s seas, cooling to the west and warming to the east. Despite this uncertainty, Hughes et al (2018) estimate that Scotland’s marine waters warmed by 0.05-0.07°C each decade between 1893 and 2016. Fig. 5 from Tinker and Howes (2020) shows the distribution of this warming, taking place around the entire Scottish coastline.
Although the Northeast region is shown to be relatively cool in fig. 4, fig. 5 shows the Northeast coast to have experienced the highest rate of warming in the country over the 1988-2017 period, at between 0.2 - 0.24°C per decade (Tinker and Howes, 2020). Looking to the future, Tinker and Howes (2020) predict a continued warming trend for the North Sea of between 2.6 and 3°C for the period of 1960 – 2099.

Impacts
Oceanic warming brings many negative impacts, both to biodiversity and to humanity. Rising ocean temperatures push native species out of their native range, while allowing invasive species adapted to warmer conditions to get a foothold, such as Pacific Oysters and Slipper Limpets (see linked sheets). These invasive organisms compete with remaining native or economically important species, damaging the industries that depend on them. 

In addition to gradual changes, worsening marine heatwave events bring short-lived, extreme heat that can wipe out marine life within their concentrated areas (Frölicher et al, 2018). Furthermore, oceanic warming is known to increase the risk of extreme weather events (Venegas et al, 2023) – patterns that have already been observed in Scotland. 2023 was found to be the wettest year on record in the country, despite also being the 13th sunniest, suggesting the multiple extreme storm events were responsible for the high volumes of rain (James Hutton Institute, 2023).