1. Introduction

  1. This Climate Change Risk Assessment (CCRA) Technical Report assesses the potential adverse effects on the Ossian Array (hereafter referred to as ‘the Array’) from climate change, in line with the United Kingdom’s (UK) guidance on CCRAs. The Technical Report will inform the assessment of climate change impacts reported in volume 2, chapter 17.
  2. The scope of the CCRA is defined in accordance with the Climate Change Committee (CCC) recommendations (CCC, 2021). This technical report considers the climate-related physical risks on the Array and identifies the current and anticipated risks throughout its 35 year lifetime. This technical report evaluates the processes utilised for managing the risks through four key stages:
  • an assessment of the baseline environment to understand present day vulnerability and assess current climate-related risks, opportunities, and levels of adaptation;
  • an assessment of the future baseline, using climate projections to understand future vulnerability and adaptation for Scotland and the UK;
  • identify vulnerability of the Array components to climate change and undertake an assessment of their likelihood and severity; and
  • review potential adaption and mitigation options.

1.1. Project Summary

  1. The Array covers approximately 858 km2 and is located in the North Sea, off the east coast of Scotland, approximately 80 km south-east from the nearest point of Aberdeen. The Array will comprise of the wind turbines (alongside their floating substructures, anchors and mooring lines), the fixed bottom Offshore Substation Platforms (OSPs), and inter-array and interconnector cables. The Applicant intends to commence the construction phase of the Array in 2031, with the intention to be fully operational by 2039 following an eight year construction programme. The initial operating lifetime is intended to be 35 years (refer to volume 2, chapter 3).

1.2. Study Area

  1. Figure 1.1   Open ▸ illustrates the climatic effects study area for the Array which encompasses the proposed Array area (i.e. the area in which the wind turbines and associated infrastructure will be located).

Figure 1.1:
Climate Effects Study Area

Figure 1.1: Climate Effects Study Area


2. Baseline Environment

2.1. Methodology

  1. To understand the impact on the Array from climate change, the baseline environment must be considered. This includes both the current baseline, and the future baseline as determined by climate projections.
  2. Current baseline offshore climatic conditions have been sourced from observational data collated within the UK Offshore Energy Strategic Environmental Assessment (Department for Business, Energy and Industrial Strategy (BEIS), 2022) and Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Reporting of the physical science (IPCC, 2021). Information has also been drawn from volume 3, appendix 7.1 where relevant, in order to provide baseline information specific to the climatic effects study area.
  3. It is established that climate change is already taking place in the UK, according to academic research (IPCC, 2021) and in legislation and policy (HM Government, 2008; Scottish Government, 2009; HM Government, 2022; BEIS, 2022). The risks associated with rising temperatures, more frequent extreme weather patterns and rising sea levels in Scotland are presented in the Climate Change (Scotland) Act 2009 and are further investigated within section 3.
  4. The assessment of future climate has been informed by climate projections based on Representative Concentration Pathway (RCP) scenarios used by the IPCC (IPCC, 2014). The RCP scenarios describe different climatic futures, all of which are considered possible depending on the volume of Greenhouse Gases (GHGs) emitted. These provide the basis for future assessments of climate change and possible response strategies, thereby giving a low to high range in potential global GHG reduction initiatives and resulting rate of climatic effects over a given period.
  5. Climate projections outlined below have been informed by the emissions scenario RCP8.5, which is a high-emissions scenario assuming ‘business as usual’ growth globally, with little additional mitigation[1]. This is a conservative (maximum design scenario) approach for the assessment, consistent with guidance set out in Institute of Environmental Management and Assessment (IEMA) (2020). Data is largely available for the end of the 21st Century. Whilst this is outside of the lifetime of the Array, these climate projections display climate trends that will begin to be felt throughout this century.
  6. The climate projections used to inform this assessment are contemporary to the time the assessment was undertaken. It can be expected that projections of future climate will evolve due to improvements in climate modelling and scientific understanding of climate systems, alongside improved data regarding the rate of change of global atmospheric carbon dioxide (CO2) and other GHGs. As such, there is some inherent uncertainty in the projections used. However, in line with relevant guidance (IEMA, 2020), a maximum design scenario has been used to account for such uncertainty. Ensuring the Array is resilient to worst-case future climate projections will ensure that it will be resilient to any shorter term climate fluctuations or variations in the climate not identified by projections (i.e. regarding rate of change).
  7. Climate projections specific to offshore UK waters have been sourced from the United Kingdom Climate Projections 2018 (UKCP18) Marine Report (Palmer et al., 2018) and are interrogated within the UK Climate Risk Independent Assessment (CCRA3), Chapter 4: Infrastructure (Jaroszweski et al., 2021). The climate projections contained in these reports have been used to examine future trends for wind speed, wave height and sea levels for offshore UK waters. Additional information at a regional (northern European) and global level has been taken from the IPCC Sixth Assessment Report (IPCC, 2021), where national or sub-national (i.e. central North Sea) information is not available, such as sea surface temperatures, surface pH and storm occurrence.

2.2. Results

2.2.1. Current Baseline

  1. Air temperatures in the central North Sea do not tend to vary beyond the range of 0°C to 19°C, with the exception of extended periods of easterly winds which can lead to extreme cold in winter and warm conditions in summer. Mean air temperatures range from lows of 1°C in January to 16°C in July (BEIS, 2022). Global air temperatures rose by 0.85°C between 1880 and 2012, and continue to rise, with each of the last four decades warmer than any decade that preceded it since 1850. Temperatures have risen more slowly over the oceans than over land (IPCC, 2021).
  2. Annual precipitation across the North Sea varies between 340 mm and 500 mm, averaging 425 mm. Precipitation rates 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 ten to 12 days in the central North Sea (BEIS, 2022).
  3. The prevailing winds in the central North Sea are from the south-west and the north-north-east, and tend to be stronger over the open sea than at the coast owing to the lack of shelter. South and south-easterly winds may also arise and remain for as long as several weeks if an anticyclone develops over Europe. Wind strengths in winter are typically in the range of Beaufort scale four to six (6 m/s to 11 m/s) with higher winds of force eight to 12 (17 m/s to 32 m/s) being much less frequent. Winds of force 5 (8 m/s) and greater are recorded 60% to 65% of the time in winter and 22% to 27% of the time in summer. In April and July, winds are highly variable, with a greater incidence of north-westerly winds (BEIS, 2022).
  4. Within the Array, wind speeds have been recorded up to 31.5 m/s during the 1979 to 2023 period, with winds predominantly from the south-west (see volume 3, appendix 7.1). As such, the Array experiences wind conditions comparable to the surrounding area.
  5. Mean Sea Level (MSL) is a crucial element of climate change related risks for offshore wind farms, as increased sea level 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). The average rate of sea level rise increased from 1.3 mm per year between 1901 and 1971, to 1.9 mm per year between 1971 and 2006, and further to 3.7 mm per year between 2006 and 2018 (IPCC, 2021). Ice sheet and glacier mass loss were the main contributors to such global MSL rise between 2006 and 2018 (IPCC, 2021).
  6. Annual mean significant wave heights in the Array area range from 1.87 m to 2.05 m, with wave direction predominantly from the north and north-north-east. With regard to extreme weather events and wave heights, an easterly storm event occurred during November 2022, with maximum significant wave height of 8.96 m within the Array area (see volume 3, appendix 7.1).

2.2.2. Future Baseline

  1. It is virtually certain 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 RCP8.5. 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. Marine heatwaves (periods of extreme high sea temperature, defined as temperatures warmer than the 99th percentile of mean sea temperatures for the region) are also expected to increase around Europe over the 21st century (IPCC, 2021).
  2. Similarly, it is virtually certain that CO2 uptake by the ocean surface will increase (due to increased atmospheric CO2 concentrations), resulting in increased ocean acidification. CO2 uptake drives changes in seawater and calcium carbonate (CaCO3) chemistry, resulting in an overall decrease of ocean pH. Northern European sea surface pH is predicted to fall by 0.4 units by 2100 under RCP8.5 (IPCC, 2021).
  3. 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 North Sea decreasing by approximately 0.1 m. Maximum wave heights in the central North Sea are predicted to reduce by 0.5 m, which could compensate for the rise in sea level, leaving the elevation of the annual maximum wave unaffected. However, owing to variation between different models, confidence in projected sea wave height changes is low (Jaroszweski et al., 2021).
  4. Changes in maximum wind speeds associated with storm surges vary across UK waters, with changes in the order of +/- 1.5 m/s. There is little consensus between models regarding the extent and pattern of such winds in relation to climate change, though some models anticipate an increase in the days of strong winds over the UK by the end of the 21st century, compared to the start of the century (Palmer et al. 2018). As such, conservatively an increase in maximum wind speed and an increase in the number of days with strong winds should be anticipated.
  5. The frequency and amplitude of storms is anticipated to slightly increase by the middle of the 21st century and beyond for northern Europe. Clustering of storms over time may also increase in many areas in Europe. However, projections of smaller scale hazardous weather have low confidence, due to the inability of climate models to accurately simulate these phenomena (IPCC, 2021).
  6. Global MSL will continue to rise throughout the 21st century, a change that is projected within all future climate change scenarios. Under RCP8.5, the UK can expect to see sea level rise of approximately 1 m by 2100. This change is regionally variable, with a lesser impact anticipated in the north of the UK. The east coast of Scotland can expect to see a MSL rise of between approximately 0.5 m and 0.6 m by 2100 (Palmer et al. 2018), broadly comparable to an anticipated global MSL rise of approximately 0.7 m by 2100 (IPCC, 2021).