Models of Scotland's Seagreen wind farm show turbine foundations cooling summer seas by 0.1 to 0.3 degrees Celsius

The cooling figures in this study come out of a model. The 0.1 to 0.3 degree drop in summer surface temperature and the heat-wave figure are both reported as simulation results ^[8][10]. Field measurements at Seagreen, from oceanographic instruments and autonomous gliders, were used to assess and support those modelled findings ^[4].

That design suits a faint signal. According to the phys.org account, turbine effects can be about as large as natural variation in the ocean, and that may explain why earlier studies sometimes struggled to find clear changes caused by wind farms ^[3]. Observations alone would have trouble telling the two apart. So the team used the models to pick out when and where impacts were most likely, then tested them against what the instruments recorded ^[4].

The physical process is vertical stirring. The foundations add to the sea's natural mixing, carrying cooler water up toward the surface and warmer water down toward the seabed ^[9]. How much that changes the surface depends on the season, the tides and how layered the water column is ^[1]. Transitional zones between mixed and stratified waters are among the most sensitive ^[2]. In the modelled 2023 marine heat wave, cooling passed 0.5 degrees in some locations ^[10]. That is at least 1.7 times the top of the ordinary summer range ^[13].

The paper's title puts detectability first ^[11]. Michela De Dominicis of NOC, the lead author, said: "Offshore wind farm structures can increase mixing in the ocean, but this does not always lead to changes that we can easily detect. Environmental conditions determine when and where these effects are strongest." ^[5]

The practical result is a rule for monitoring. Observations targeted at strongly stratified periods are more likely to pick up changes caused by turbine structures ^[6]. De Dominicis said the combined approach "could contribute evidence to future offshore wind site planning, as well as help to inform the design and environmental monitoring." ^[14]

I think the evidence supports assessing each site against its own oceanography. The size of the effect moves with local season, tide and stratification ^[1], so a cooling figure carried from one farm to the next would misstate the change. That view comes with conditions. It rests on one farm, Scotland's largest ^[12], in what Beth Scott of the University of Aberdeen, principal investigator of PELAgIO, called "deeper, stratified waters" ^[15][7]. The report does not say how far beyond the turbine array the cooling extends.

The thing this doesn't tell you is whether a few tenths of a degree matters to anything living there. Scott said the validated modelling "is already allowing wider-scale modeling of cumulative effects of these seasonal changes on the habitats of a variety of marine animals along with comparisons of climate change effects." ^[15]