Sea levels are a combination of tidal level, surge level, mean sea level and waves and their interaction. Any change in mean sea level affects sea level directly but also modifies tide, surge and wave propagation and dissipation by changing the water depth. Local sea level is affected by ocean circulation and by geographical variations in the temperature and/or salinity of the water column. These regional influences are also likely to change under global warming. Local changes in sea level are thus a combination of global mean changes and changes in the patterns of sea level relative to the global mean.
Rising sea levels during the Holocene transgression from 15,000 to 5,000 years BP caused the Solent River valley to become drowned. Fluctuations in sea levels followed until approximately 3,000years BP. Evidence suggests a background rate of sea-level rise of approximately 1-1.5mm per annum, until the acceleration of recent decades. UK Climate Projections give details on the latest estimates for changing sea levels in the UK. Projections of UK coastal absolute sea level rise (not including land movement) for 2095 that range from approximately 13-76 cm. This rise is likely to be higher in the south of the country in areas like the Solent where the land is subsiding.
Data from the University of Southampton (2011) puts relative sea-level rise rates for Portsmouth as 1.21 +/- 0.27 mm/yr and Southampton as 1.30 +/- 0.18 mm/yr.
An evidence base is growing that shows that climate change is already having an impact on the marine environment across all the components that contribute to UK governments vision for “clean, safe, healthy, productive and biologically diverse oceans and seas” (Defra, 2008; MCCIP, 2008). Good estimates of what could happen in the future marine environment and how this might impact issues as diverse as flooding, habitat conservation and food safety are becoming of increasing importance for adaptation and risk planning.