Online Marine & coastal projections 6.1 Introduction
There is already substantial evidence for the warming of the shallow seas of the northwest European shelf over the past decades based on analysis of satellite radiometer data (e.g. Gomez-Gesteira et al. 2008) and long term monitoring of point time-series and repeat sections (Hughes and Holliday, 2006; van Leussen et al. 1996). Trends in the salinity are less clear, but the evidence suggests a freshening to a minimum in the 1980s–1990s followed by an increase in salinity after that (Evans et al. 2003; Holliday et al. 2008a). However, year-to-year variations tend to dominate the salinity variability.
Here we use a numerical model to investigate how climate forcing late in the 21st century might influence the hydrography and circulation of the northwest European continental shelf seas. Particular emphasis is placed on the surface and near sea bed temperature and salinity, the stability of the water column, and the volume transports across a number of key sections shown on Figure 6.1. The future period of interest is 2070–2098 and is compared with conditions typical of 1961–1990, the UKCP09 baseline.
Investigations of climate change impacts on the hydrography and circulation of shelf seas are at an early stage of development. Hence, the conclusions reached here are tentative, exploring possibilities rather than trying to make precise predictions. As a first look, we have limited our investigation to the two time periods mentioned above. The scenario forcing is derived from the Met Office Hadley Centre Regional Climate model (HadRM3), which in turn is forced by a mid climate sensitivity member of the coupled global climate model PPE ensemble (specifically the unperturbed member) using the UKCP09 Medium emissions scenario (SRES A1B). However, we anticipate that further simulations will be carried out using a range of ensemble members to better quantify uncertainty, in a similar way to that used for investigating coastal flooding by storm surges. The experimental set-up of the driving RCM is described more fully in Chapter 2.