Sea level rise and shelf seas

Sea level rise is expensive, both in terms of the damage it will cause, and the cost of defending against it. Reducing uncertainty in projected changes in sea level allows for the most appropriate and cost effective adaptation measures to be taken. There are two aspects of sea level that are of interest: the mean sea level (the sea level averaged over the tidal cycle) and extreme sea level (typically the maximum sea level experienced during storm events). Under global warming there could be changes in both of these.

There are two main mechanisms which give increases in global average sea level: thermal expansion of the warming oceans, and addition of water to the oceans (predominantly from melting glaciers, ice sheets and icecaps). There is a spatial pattern to sea level rise which will lead to some parts of the world experiencing greater or less than the global average sea level rise. Changes in the absolute sea level (i.e. relative to the centre of the Earth) at a particular location are further modified by vertical land movements to give relative sea level rise - what is experienced on the coast.

Storm surges are the major process that leads to extremes in sea level. They result from sea level rising due to a combination of a reduction in atmospheric pressure, water being piled up on the coast by the wind, and in some cases funnelling by the local bathymetry. The climatology of storm surges will be affected by climate change which can alter the frequency and intensity of the storms that cause these surges.

Other marine impacts arising with climate change relate to changes in the wave climatology and in ocean fields such as temperature and salinity (and associated vertical stratification) and circulation. These changes in the physical environment then cascade down to affect the marine ecosystems.

We are currently working on many of aspects of these problems. For our work on projects such as Thames Estuary 2100 (TE2100) and United Kingdom Climate Projections 09 (UKCP09) we have provided state of the art projections of mean and extreme sea level rise for the UK.

Key aims

• Improve projections of sea level rise - potential use of observational constraints and better modelling of land-based ice masses
• Understand changes in storminess that alter surge and wave. climatology
• Improve uncertainty estimates for changes in wave climatology and provide an uncertainty estimate for changes in shelf sea temperature and salinity
• Work to provide likely changes in ocean acidification, water quality measures and ecosystem response
• Link to impacts on communities, the environment and the economy. Work on adaptive solutions to minimise these impacts
• Close engagement with users and stakeholders

Current projects

• Estimating uncertainty in the UKCP09 projection for the shelf seas oceanography and wave climatology by running additional ensemble members of the shelf sea model POLCOMS and wave models (WAM or NWW3) within the Met Office Hadley Centre.
• Making projections of ecosystems, nutrient loading and acidification of the north-west European shelf: the shelf seas model POLCOMS can drive the model ERSEM to give projections of the biological and chemical response to climate change. 
• Building stronger links with users, stakeholders, government and the wide marine community. We are now playing an active role within the Marine Climate Change Impact Partnership (MCCIP), and are developing links with other external groups.