17.7. Baseline Environment

17.7.1. Overview of Baseline Environment

  1. The following sections provide a summary of the climatic effects baseline environment. The GHG technical report (volume 3, appendix 17.1) and CCRA technical report (volume 3, appendix 17.2), includes full details of the analysis undertaken to develop the climate change risk and GHG emissions baseline.

                        GHG Emissions Assessment Baseline Environment

  1. To determine the GHG emissions assessment baseline environment, information has been sourced and cross referenced from the benthic subtidal ecology technical report (volume 3, appendix 8.1).
  2. The baseline consists of various subtidal habitats which have been classed according to sediment type using the Folk (1954) classification, as set out in volume 2, chapter 8. The predominant sediment types are muddy sand, sand and slightly gravelly sand. These sediments are likely to contain stores of ‘blue carbon’, which is organic carbon that has been captured and stored through biological processes in the coastal and marine environment (Cunningham and Hunt, 2023). Though subtidal sediments are a large carbon store within Scottish Exclusive Economic Zone (EEZ) waters, with an estimated 357 mega tonnes (Mt) of organic carbon stored within coastal and marine sediments (Smeaton et al., 2020), such subtidal habitats are likely to present carbon stores of low relative importance, given their low organic carbon storage density compared to other habitats, including saltmarsh and seagrass habitats. Section 17.11.1 presents the standing blue carbon stock in the subtidal sediments present within the Array.
  3. The Array will likely contribute to the abatement of the amount of fossil fuel generation within the UK Grid (i.e. UK Grid carbon intensity). As such, the current baseline with regard to UK Grid-average emission factor for electricity generation, without the Array, is 252.97 kgCO2e/MWh (including well-to-tank but as-generated, i.e. excluding transmission and distribution losses) (DESNZ and Defra, 2023).
  4. Further information is presented in the GHG technical report (volume 3, appendix 17.1).

                        CCRA Baseline Environment

  1. Baseline offshore climatic conditions for the climatic effects study area have been sourced from observational data collated within the UK Offshore Energy Strategic Environmental Assessment (BEIS, 2022c), IPCC Sixth Assessment Reporting of the physical science (IPCC, 2021) and relevant information included in the physical processes technical report (volume 3, appendix 7.1).
  2. Mean air temperatures in the central North Sea (where the Array is located) range from lows of 1°C in January to 16°C in July, with surface air temperatures exceeding sea surface temperatures during the spring and summer months and falling below sea surface temperatures during the autumn and winter months (BEIS, 2022c). Global air temperatures rose by 0.85°C between 1880 and 2012, and continue to rise (IPCC, 2021).
  3. Precipitation rates within the central North Sea follow a seasonal trend with April to June tending to be the driest months, and October to January being wetter. Thunderstorms are infrequent, and snow showers vary from approximately 10 to 12 days per year in the central North Sea (BEIS, 2022c).
  4. Within the climatic effects study area, wind speeds have been recorded up to 31.5 m/s during the 1979 to 2023 period, with winds predominantly from the south-west. Annual mean significant wave height ranges from 1.87 m to 2.05 m, with wave direction predominantly from the north and north-north-east. An easterly storm event occurred within the climatic effects study area during November 2022, with maximum significant wave height of 8.96 m (volume 3, appendix 7.1).
  5. Mean sea level (MSL) is a crucial element of climate change related risks for offshore wind farms, as increased MSL has the potential to both increase water damage and corrosion of components above the water line at time of construction, and/or increase mooring line tension. MSL rise also has the potential to cause increased damage from storm surge. Global MSL rose by 0.2 m between 1901 and 2018, and continues to rise (IPCC, 2021).
  6. Further information is presented in the CCRA technical report (volume 3, appendix 17.2).

17.7.2. Future Baseline Scenario

  1. The EIA Regulations require that “a description of the relevant aspects of the current state of the environment (baseline scenario) and an outline of the likely evolution thereof without implementation of the project, as far as natural changes from the baseline scenario can be assessed with reasonable effort, on the basis of the availability of environmental information and scientific knowledge” is included within the Array EIA Report.
  2. If the Array does not come forward, an assessment of the ‘without development’ future baseline conditions has also been carried out and is described within this section.

                        GHG Emissions Assessment Future Baseline

  1. The future baseline GHG emissions for existing land use (seabed) without the Array are expected to remain similar to that listed in paragraph 22. Some areas of the North Sea experience almost no sediment accumulation and associated carbon sequestration through organic carbon deposits (Cunningham and Hunt, 2023). As such, no material change to the blue carbon stored within the Array area is anticipated in the future baseline.
  2. The future baseline for electricity generation that would be displaced by the Array depends broadly on future energy and climate policy in the UK, and more specifically (with regard to day-to-day emissions) on the demand for operation of the Array compared to other generation sources available, influenced by commercial factors and National Grid’s needs.
  3. Several future baseline scenarios have therefore been considered using DESNZ projections of the carbon intensity of long-run marginal electricity generation during the Array’s operating lifetime (DESNZ, 2023a) and assumptions about specific generation sources that could be displaced. These are detailed in the GHG technical report (volume 3, appendix 17.1).
  4. The carbon intensity of baseline UK Grid electricity generation (see paragraph 23) is projected to reduce over time and so too would the intensity of the marginal generation source, displaced at a given time.

                        CCRA Future Baseline

  1. In the near future (the next decade to two decades), variations in average temperature and precipitation will likely be the most visible year-to-year changes in climate. In subsequent decades, within the operating lifetime of the Array, anthropogenic climatic changes are expected to become more apparent.
  2. It is expected that sea surface temperatures will continue to increase in the 21st century, with global mean sea surface temperatures predicted to increase by approximately 2.9°C by 2100 under Representative Concentration Pathway (RCP) 8.5[1]. Sea temperatures in Northern Europe (including the North Sea) are predicted to rise at a greater rate than the global average, with temperatures predicted to increase by approximately 3.4°C under RCP8.5 in the same time period. Ocean acidification is anticipated to increase, with a fall in surface pH by 0.4 units by 2100 under RCP8.5 (IPCC, 2021).
  3. Average sea level rise around the UK is expected to increase by 1 m by 2100, though a lesser rise is anticipated in the north of the UK. The east coast of Scotland can expect to see an average sea level rise of approximately 0.5 m to 0.6 m by 2100 (Palmer et al, 2018). The average wave height is predicted to decrease around much of the UK at a factor of about 10% to 20% over the 21st century, with average wave heights in the central North Sea predicted to reduce by 0.5 m. However, owing to variation between different models, confidence in projected sea wave height changes is low (Jaroszweski et al., 2021).
  4. Further information has been presented within the CCRA technical report (volume 3, appendix 17.2).

17.7.3. Data Limitations and Assumptions

  1. There is uncertainty about future climate and energy policy and market responses, which affect the likely future carbon intensity of energy supplies, and thereby the future carbon intensity of the electricity generation being displaced by the Array. UK Government projections consistent with national carbon budget commitments have been used in the assessment (‘long-run marginal’ projections). It should be noted that latest UK Government projections include an increase in renewable energy generation, in particular from increased offshore wind capacity (DESNZ, 2023a), consistent with the UK Government’s current policy of a low-carbon electricity grid by 2035 with no unabated fossil fuel generation (BEIS, 2021). Thereby, for the Array’s operational lifetime, the long-run marginal projections presented are reliant on offshore wind projects such as the Array being brought online. As such, the long-run marginal does not represent a true ‘without development’ future baseline. Additionally, there is inherent uncertainty in such projections as the UK grid electricity factor changes from year to year as the fuel mix consumed in UK power stations changes, and as the proportion of net imported electricity also changes. Annual fluctuations can be large as they depend on the relative prices of coal and natural gas, alongside fluctuations in peak demand and renewable provision (DESNZ, 2023). Therefore, multiple scenarios have been considered to present a likely range of avoided emissions, including displacement of non-renewable fuels as an upper estimate for the likely avoided emissions, and comparison to the long-run marginal projections as a lower estimate.
  2. Construction phase GHG emissions associated with the manufacturing of infrastructure associated with the Array may occur outside the territorial boundary of the UK and hence outside the scope of the UK’s national carbon budget, policy and governance. However, in recognition of the climate change effect of GHG emissions (globally occurring), and to avoid ‘carbon leakage’ overseas when reducing UK emissions, emissions associated with the construction phase have been presented within the assessment and quantification of GHG emissions, as part of a life cycle GHG emission assessment of the Array (see paragraph 62).
  3. The specific design for the components of the Array (floating wind turbines, mooring and anchoring systems, OSPs, inter-array and interconnector cabling), alongside the specifications of vehicles and vessels that would be used by the Array have not yet been specified. Thus, there is a degree of uncertainty regarding GHG emissions resulting from the manufacturing and construction of wind turbines and infrastructure, vessel movements and operation and maintenance activities associated with the Array. This assessment seeks to limit the impact this might have by using maximum design scenario (MDS), which includes material quantities and material types (i.e. those with the greatest carbon impact), in the calculation of construction phase emissions and emissions resulting from operation and maintenance activities. This assessment has also used MDS vessel movements, as stated in Table 17.7   Open ▸ , and does not account for future decarbonisation of these vessel movements. It is unlikely that the full extent of these MDS material quantities will be used in the final design of the Array, owing to improvements in wind turbine and associated infrastructure design, refinements to design assumptions and continued decarbonisation of the manufacturing and transport sectors. As such, calculated emissions represent a conservative (reasonable adverse case) scenario.
  4. Detailed information is not yet available for the decommissioning phase. However, it is anticipated that this phase will involve similar types and numbers of vessels and equipment to that of the construction phase. As such, emissions from the decommissioning phase have been estimated based on MDS vessel movements for the construction phase.
  5. Blue carbon that is released as a result of marine habitat disturbance dissolves into coastal and marine ecosystems, such as the ocean. As such, this impact does not directly contribute to the global atmospheric mass of CO2 (the receptor). However, it is likely to indirectly impact atmospheric CO2 concentrations, as an increased concentration of dissolved CO2 alters ocean and calcium carbonate (CaCO3) chemistry. Though interactions between different states of carbon in the oceans is complex, it is likely that increased concentrations of ocean CO2 will overall reduce the capacity of oceans to absorb CO2 and cause a greater potential for the ocean to release CO2 to the atmosphere under certain conditions (IPCC, 2021). As such, for the purposes of this assessment remineralisation of blue carbon stocks has been assumed to have the same impact as the release of an equivalent mass of CO2 to the global atmosphere.
  6. An assumed operational lifetime of 35 years (2038 to 2072) has been applied to the assessment of avoided GHG emissions associated with the operation and maintenance phase of the Array and consideration of maintenance activities.
  7. When assessing climate risks, uncertainty arises from both modelling uncertainty and natural variability in the potential magnitude of future changes in climate. A high magnitude of change scenario and the high end of probabilistic projections have therefore been used, to provide a precautionary reasonable adverse approach. This is further discussed in the CCRA technical report (volume 3, appendix 17.2).
  8. The above uncertainties are integral to the assessment of climatic effects, but a precautionary approach has been taken as far as practicable to provide a reasonable worst-case assessment. On the basis of the above, it is considered that limitations to the assessment have been reduced and that the results provide a robust estimate of the effects of the Array.
  9. It is important to note that the Array would not operate in isolation, as transmission infrastructure is required to connect the Array to the grid in order to realise the potential avoided emissions associated with the production of wind energy. However, the proposed offshore export cable corridor(s) and proposed onshore transmission infrastructure are subject to separate applications. As such, it is necessary to consider the embodied emissions of the transmission infrastructure within the cumulative assessment, so as to understand the whole-life effects of Ossian.
  10. The design parameters of the associated proposed offshore export cable corridor(s) and proposed onshore transmission infrastructure are not yet available. As such, calculations for the assessment of cumulative effects, in order to quantify whole-life GHG emissions for Ossian, have been based on high-level indicative parameters provided by the Applicant. These parameters will be refined in subsequent applications for the transmission infrastructure, alongside the associated calculations as more information becomes available. The cumulative assessment presented in section 17.12 is therefore carried out using a precautionary approach and is a maximum design scenario.
  11. It is worth noting that a high level of conservatism has been used to derive the GHG calculations, as detailed in volume 3, appendix 17.1, as these are based on the current understanding of required materials for the Array, which are likely to be further refined during final stage design. In addition, the assessment included in this EIA chapter applies another layer of conservatism, as it is based on the most adverse scenario, leading to a precautionary assessment.