Use of Baltic Sea modelling to investigate the water cycle and the heat balance in GCM and regional climate models

Abstract

Results from the first simulations with the Rossby Centre regional climate atmosphere (RCA) model were used to force 2 versions of process-oriented models of the Baltic Sea -one timedependent, the other considering the mean state. The purpose was primarily to obtain a first scenario of the future state of the Baltic Sea. In addition, we looked at this exercise as a method to evaluate the consistency of the water cycle and the heat balance produced by atmospheric climate models. The RCA model is a high-resolution atmospheric regional model which is forced with lateral conditions from a global model. A large-scale Baltic drainage basin hydrological model, forced by the RCA model, was used to simulate river runoff. Using RCA model data from the control run we found that that the temperature and ice conditions in the Baltic Sea were reasonably realistic while the salinity field was poorly reproduced. We conclude that the modelling of the water cycle needs considerable improvement. We also conclude that the time for the Baltic Sea to respond to the water cycle is much longer than the integration period so far used with the RCA model. Forcing the ocean models with RCA model data from a future scenario with an enhanced greenhouse effect gives an increased sea-surface temperature and a much reduced extent of ice in the Baltic Sea due to climate warming. Also the salinity is reduced, which implies possible serious effects on the future marine life in the Baltic Sea. The results demonstrate that accurate atmospheric modelling of not only the heat balance but also the water cycle is crucial for Baltic Sea climate simulations.

Multimodel estimates of the changes in the Baltic Sea ice cover during the present century

“…Despite these drastic reductions, no totally ice-free winters were simulated to occur during 2071Á2100. In contrast, in a model experiment conducted by Omstedt et al (2000), there was almost no ice in 3 out of 10 winters.…”

“…Previous estimates of the sensitivity of the Baltic Sea ice cover to climatic changes have been based on numerical modelling (Omstedt and Nyberg, 1996;Haapala and Leppa¨ranta, 1997;Omstedt et al, 2000;Haapala et al, 2001;Meier et al, 2004;Meier, 2006) or on using statistical methods to correlate sea ice variability to atmospheric conditions (Tinz, 1996;Omstedt and Chen, 2001;Jylhaë t al., 2008;Luomaranta et al, 2010). In conjunction with projections of future warming, considerable thinning of the ice and shrinking of the ice cover, as well as a shortening of Decade 1 9 0 1 -1 9 1 0 1 9 1 1 -1 9 2 0 1 9 2 1 -1 9 3 0 1 9 3 1 -1 9 4 0 1 9 4 1 -1 9 5 0 1 9 5 1 -1 9 6 0 1 9 6 1 -1 9 7 0 1 9 7 1 -1 9 8 0 1 9 8 1 -1 9 9 0 1 9 9 1 -2 0 0 0 2 0 0 1 -2 0 1 0 the ice season in the Baltic Sea, are foreseen in these studies, but there are differences in the strength of the responses.…”

Long‐term Changes and Impacts of Hypoxia in Danish Coastal Waters

“…Combined with high TN input from land, these temperature changes could be crucial to the benthic fauna. Given that river runoff and temperature are projected to increase drastically over this century due to global warming (Omstedt et al 2000), hypoxia will probably become more severe in the future, with increases in nutrient input and stratification. The 18C increase in temperature observed in the Skagerrak (Fig.…”

Future changes in the Baltic Sea acid–base (pH) and oxygen balances

“…As climate models applied on a regional scale have deficits in both their water and heat balances (e.g. Omstedt et al, 2000;BACC Author Team, 2008;Meier et al, 2011), we apply the so-called delta-change bias correction. Correction factors (anomalies) were determined based on the difference between the climate model control simulation and observations, averaged over the 1961Á1990 control period.…”