Projection of physical conditions in the North Sea for the 21st century

Abstract

A global climate scenario run based on the IPCC future emission scenario SRES A1B was dynamically downscaled for the North Sea, using an uncoupled meso-scale model system. The atmospheric forcing shows an increase in air temperature during the 21st century with stronger warming in winter than in summer. These trends are reflected by an increase in annual mean sea surface temperature of ~1.8°C. The strong warming in winter is the main driver for the total warming of the North Sea, as indicated by the analysis of surface heat flux components. The thermocline weakens in intensity according to the changing temperature profiles, and its mean depth slightly decreases due to lower wind speeds. The salinity in the North Sea drops by ~0.6 psu because of decreasing salinity of the inflowing Atlantic waters, increasing Baltic discharge, and higher downward surface fresh water fluxes. Some of our results disagree with other dynamical downscaling studies, as the results depend on the parent global model. In general, the downscaled projected trends qualitatively agree with the results of the coarser global model. Nevertheless, in particular, the magnitudes of the surface heat fluxes, the formation of the frontal system, and the strength and structure of the general circulation are more realistically represented in the regional meso-scale model. KEY WORDS: Dynamical downscaling · North Sea · IPCC SRES A1B · Climate changeResale or republication not permitted without written consent of the publisher CLIMATE RESEARCH

Projected Change—North Sea

“…All models show an All scenario simulations are forced by IPCC-AR4 generation GCMs and ESMs area-averaged monthly mean SST increase of 1.7-3.0°C for the end of the century (Fig. 6.9) and annually average SST increases of about 2°C (Bülow et al 2014), which is very similar to uncoupled downscalings forced by the ECHAM5/MPIOM model reported by Wakelin et al (2012a), and Mathis and Pohlmann (2014). However, the uncertainty range arising from the different regional models was significantly larger compared to uncoupled model simulations.…”

“…These experiments were performed either as time slice experiments of 20-30 years for present-day and future (end-of-the-century or middle-of-the-century) climates (Ådlandsvik 2008;Holt et al 2010Holt et al , 2012Holt et al , 2014Holt et al , 2016Friocourt et al 2012;Wakelin et al 2012a;Pushpadas et al 2015) or as continuous integrations (e.g. Gröger et al 2013;Bülow et al 2014;Mathis and Pohlmann 2014). Only one downscaling was performed for the SRES A2 scenario, which considers stronger radiative forcing (Madsen 2009).…”

“…In contrast, the seasonal maximum thermocline depth showed a clear and strong deepening trend. Mathis and Pohlmann (2014) attributed this to a delay in thermocline erosion south of the 50 m depth contour in autumn, caused by a decrease in seasonal heat loss and wind speeds in the future (Fig. 6.19).…”

“…Alternative metrics are the depth and strength of the thermocline, which could also provide insight into the nature of the change. Using these metrics and Mathis and Pohlmann (2014) identified a weak shallowing of the thermocline in the HAMSOM projection, which they attributed to a weakening of summer wind speeds. In contrast, the seasonal maximum thermocline depth showed a clear and strong deepening trend.…”

“…A detailed investigation of transport change was undertaken by and Mathis and Pohlmann (2014) based on one regional scenario only. Projected future changes in circulation were analysed for seasonal mean current velocity vectors and trend analyses were applied to depth-averaged current speeds and to volume transports through various lateral sections in the North Sea.…”