Modeling the combined impact of changing climate and changing nutrient loads on the Baltic Sea environment in an ensemble of transient simulations for 1961–2099

H E M Meier,B G Gustafsson,H C Andersson,K Eilola,S Schimanke,A Höglund,R Hordoir,C Dieterich

doi:10.1007/s00382-012-1339-7

H E M Meier, B G Gustafsson + Show 6 more

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https://doi.org/10.1007/s00382-012-1339-7

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Abstract

The combined future impacts of climate change and industrial and agricultural practices in the Baltic Sea catchment on the Baltic Sea ecosystem were assessed. For this purpose 16 transient simulations for 1961–2099 using a coupled physical-biogeochemical model of the Baltic Sea were performed. Four climate scenarios were combined with four nutrient load scenarios ranging from a pessimistic business-as-usual to a more optimistic case following the Baltic Sea Action Plan (BSAP). Annual and seasonal mean changes of climate parameters and ecological quality indicators describing the environmental status of the Baltic Sea like bottom oxygen, nutrient and phytoplankton concentrations and Secchi depths were studied. Assuming present-day nutrient concentrations in the rivers, nutrient loads from land increase during the twenty first century in all investigated scenario simulations due to increased volume flows caused by increased net precipitation in the Baltic catchment area. In addition, remineralization rates increase due to increased water temperatures causing enhanced nutrient flows from the sediments. Cause-and-effect studies suggest that both processes may play an important role for the biogeochemistry of eutrophicated seas in future climate partly counteracting nutrient load reduction efforts like the BSAP.

Highlights

For the Baltic Sea (Fig. 1) regional climate modeling results suggest that global warming may cause increased water temperatures and reduced sea ice cover combined with reduced salinity due to increased wind speeds and increased river runoff (e.g. BACC author team 2008; Meier et al 2006)
We focus on ocean modeling results of the four transient simulations at selected monitoring stations in the Baltic proper and Gulf of Finland (Fig. 1)
The quality of the HadCM3 driven simulation is worse mean vertical temperature profiles are slightly better reproduced in the HadCM3 driven simulation than in ECHAM5 driven simulations because of a warm bias in ECHAM5 over the Baltic Sea (Meier et al 2011c)

Summary

Introduction

For the Baltic Sea (Fig. 1) regional climate modeling results suggest that global warming may cause increased water temperatures and reduced sea ice cover combined (eventually) with reduced salinity due to increased wind speeds and increased river runoff (e.g. BACC author team 2008; Meier et al 2006). The projected hydrographic changes could have significant impacts on the marine ecosystem. To estimate these effects and to calculate the impact of nutrient load reductions in future climate an ensemble of model simulations for the period 1961–2099 were carried out. Ensemble simulations are necessary to estimate uncertainties of projections Uncertainties are caused by biases of global and regional climate models and by unknown socio-economic future developments with impact on greenhouse gas emissions, nutrient loads from land and atmospheric deposition. For the marine environment of regional seas only a few studies on uncertainties of future projections are available Neumann (2010) studied the results of two transient simulations with a coupled physical-biogeochemical model

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