How is climate change affecting coastal flooding in the UK?
Climate change is causing sea level rise, which is increasing the risk of flooding around the UK’s coastline. It is also increasing coastal erosion. Both of these hazards pose a risk to people and the environment.
Why is sea level rising globally and by how much?
Rising global temperatures are leading to global sea level rise by causing the melting of glaciers and the land-based ice sheets in polar regions, as well as the thermal expansion of ocean water. Since 1993, global sea level has been monitored by satellites, which show that it is currently rising at an average of 3.3 millimetres per year, an acceleration from the rate of 1.4 millimetres per year, which was the average calculated for the 20th century.
The most recent assessment by the Intergovernmental Panel on Climate Change (IPCC), in 2013, of potential sea level rise as a result of global warming induced by climbing greenhouse gas emissions found that the total increase would likely (i.e. with a probability of 66 per cent) be between 260 and 820 millimetres by the last decades of this century compared with the last decades of the 20th century. The precise amount will depend on emissions levels in the period to 2100. These estimates are due to be updated by the IPCC in 2021.
What are the impacts on the UK?
The actual impact on sea levels around the UK coastline depends on several factors, including the Earth’s rotation, oceanic circulation and local geological changes. A major factor for the UK is that the land is still adjusting very slowly to the retreat of the ice sheets at the end of the last Ice Age, which ended around 12,000 years ago: parts of Southwest England are sinking at a rate of about 0.6 millimetres per year, while parts of Scotland are rising by 1 millimetre per year. Thus while sea level rise is happening around the entire UK coast, it is most rapid in Southwest England.
The Met Office has projected sea level rise around the UK that might occur by 2100, showing the possibility of increases of more than a metre in many locations in a high-emissions scenario that leads to greater warming.
The major impacts of sea level rise occur during high tides and storms, causing flooding along coastlines and estuaries. In 2018 the Climate Change Committee (CCC), the Government’s independent advisers on climate change, said that by the 2080s in England, “up to 1.5 million properties, including 1.2 million homes, may be in areas at significant level of [coastal] flood risk”.
Sea level rise can also increase coastal erosion because waves can extend further up and along beaches and cliffs. Erosion is happening faster along coastlines made from softer sediments, notably on the East coast of England, where households and businesses in areas most at risk may find it hard to buy insurance. The CCC estimates that more than 100,000 properties in England may be at risk from coastal erosion by the 2080s.
Both flooding and erosion place property, farmland, infrastructure including ports, roads and railways, and also natural habitats at risk. In some locations, such as the densely populated and low-lying Thames Estuary, concentrated large numbers of people and critical national infrastructure are vulnerable to these impacts.
Managing the risk
There are many ways in which the UK can adapt to these growing impacts. These include using ‘hard engineering’ to maintain and strengthen existing structures such as sea walls in a policy approach called ‘hold the line’, and building new defences further out from the coastline to ‘advance the line’. The Southsea coastal scheme on the Hampshire coast is currently the largest local authority-led project to strengthen coastal defences, aiming to reduce the threat of flooding to around 10,000 homes and 700 businesses.
Alternatively, a policy of ‘managed realignment’ may be taken, where the shoreline is allowed to move backwards (or forwards) naturally to an agreed position, with management to control the extent. This may be appropriate in locations that are considered too difficult to protect with hard engineering or where the economic cost of protection would outweigh the benefit – for example, where the population density is low or where there are few businesses to protect; for instance, Gwynedd Council has raised concerns about the feasibility and cost of protecting the shoreline around the village of Fairbourne on the North Wales coast.
Restoring coastal environments such as saltmarshes can also protect the coast as the natural feature acts as a barrier to the sea, dissipating waves’ energy and reducing the risk of erosion and of flooding further inland. This approach also has the advantage of creating or improving wildlife habitats. Saltmarshes may form as a result of managed realignment.
Each of the devolved administrations of the UK has developed plans and strategies for managing coastal flood risk. In July 2020, the Environment Agency published its National Flood and Coastal Erosion Risk Management Strategy for England, with a vision for “a nation ready for, and resilient to, flooding and coastal change – today, tomorrow and to the year 2100”. It states: “In the face of a changing climate, we need to also make our places more resilient to flooding and coastal change, so that when it does happen it causes much less harm to people, does much less damage, and ensures life can get back to normal much quicker.”
This Explainer was written by Bob Ward with Georgina Kyriacou.