The built marine environment includes a wide range of structures that could potentially be impacted by climate change in a number of different ways. For the purposes of this review the built environment has been split into offshore and coastal structures.

The design of structures is traditionally based on an analysis of comprehensive metocean parameters from which future extreme events are derived. With the uncertainties introduced by climate change this technique may become less effective at predicting future extreme conditions and the modelling of climate change impacts will need to be explored.

The impacts of climate change on marine structures are diverse and depend on the type of structure, its function and location within the marine environment.

100-year analyses of both mean and significant wave heights are typically used to inform design criteria for offshore built structures such as oil installations. These studies reveal a high degree of natural variability in wave climate, which makes interpreting the impacts of climate change on offshore built structures very difficult.

There is limited published evidence that climate change has led to the offshore industry having to adjust any operational practices over the recent past or the present day.

There is no published evidence that specifically relates climate change to impacts on coastal structures over the recent past or the present day. However, sea-level rise has affected the planning of coastal structures.

Overall expected impacts can be summarised as follows:

• Increases in wave energy and the frequency of storm events leading to greater stresses on both offshore and coastal structures and associated access and maintenance problems
• Changes in tidal currents leading to changing scour and erosion patterns around both offshore and coastal structures
• Increases in sea level and wave heights leading to more frequent overtopping of defences and flooding of the coastal zone
• Based on the UKCP09 projections only, built structures located in the southern North Sea and the Irish Sea and North Channel regions will be impacted the most by changes in winter significant wave height.

Any reduction in the area of intertidal habitats (mudflats, saltmarsh) as a result of climate change would result in increased stresses on coastal structures as these natural defences tend to dissipate wave and tidal energy.

In addition, high value infrastructure exists on the coastline, such as power stations, ports, rail and road. These structures will have a requirement to be maintained into the future and consequently require a commitment to continued protection from coastal processes. Nuclear power installations in particular will require particularly long-term commitments as the life cycle of a power station is measured in centuries.

What is already happening: Low

What could happen: Low

There is a general lack of data throughout entire sector on both past and future impacts. Coastal impacts are generally better researched and understood than offshore impacts. This could be due to the relatively shorter life cycles of offshore structures compared to coastal structures.

The top priority knowledge gaps that need to be addressed in the short term to provide better advice to be given to policy makers are:

1.  Impacts of climate change on sediment transport processes and morphology. For example it would be useful to relate the UKCP09 outputs to sediment transport and morphological processes.
2. Lack of long-term records with which to assess past trends in oceanographic processes.
3. More information on changes to wave period as well as wave height would be beneficial in identifying future impacts on structures in the marine environment.

Offshore structures

The expected life of an offshore structure is currently around 20 years (Rees, 2008), the lifespan of offshore installations is also dependant on the reserves of fossil fuels in UK waters. Increased stresses on offshore structures will increase the cost of retrieving fossil fuels and generating renewable energy, the potential cost increase has not been quantified in the available literature.

Coastal Structures

It has been calculated that in terms of economic losses in the future the potential effects of coastal erosion on its own are minor compared to flooding and represent only 2-6% of total potential losses (Halcrow, 2001; Hall et al., 2006). However, coastal erosion in the context of other coastal issues and the viability of property and infrastructure on eroding coastlines still merits serious attention (Hall et al., 2006).

Figures are only available for both river and coastal combined and are not available exclusively for the coastal zone. Currently, flood and coastal defences cost approximately £464 million within the UK (Foresight, 2004). Engineering to address future flood risk could amount to between £22 and £75 billion by the 2080s depending on the scenario. As an example, in 20 years time the annual cost of flood and coastal defences would need to be between £700 million and £1.1 billion per year (Defra, 2004a). It is important to remember that the above costs are for flooding on both rivers and the coast.

An assessment of coastal erosion defence costs was undertaken by Defra (2004b) and showed that the cost of maintaining all defences at the current standard regardless of the benefit cost amounted £2.9 billion over the next 100 years at present value. Areas under the greatest threat from future erosion will be along major estuaries and the east coast (Foresight, 2004). Present levels of expenditure on coastal defence will not keep pace with future coastal erosion resulting in approximately one third of coastal defences being destroyed in the coming decades (Foresight, 2004).

Although it is useful to consider the financial costs of maintaining coastal structures it is important to also think about the social costs of protecting or not protecting communities. Government expenditure will by necessity be directed towards areas of greatest economic benefit (i.e. larger urban areas) leaving smaller communities more vulnerable to coastal change. It is likely that greater focus on management of future change through the land use planning system and other mechanisms as well as the maintenance of traditional defences may be necessary to effectively manage risk and social impacts on coastal communities.

This also relates to the identification of areas most susceptible to the impacts of climate change where the regions of greatest physical change may not necessarily coincide with regions of greatest social impact.

Hunt, S., and J. Rees (2010) Built Structures in MCCIP Annual Report Card 2010-11, MCCIP Science Review, 9pp. www.mccip.org.uk/arc