Baltic Sea climate in the late twenty-first century : a dynamical downscaling approach using two global models and two emission scenarios

• Published in: Climate dynamics Vol. 27; no. 1; pp. 39 - 68
• Main Author: MARKUS MEIER, H. E
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01.07.2006; Berlin Springer Nature B.V
• Subjects: Deep water; Earth, ocean, space; Exact sciences and technology; External geophysics; Freshwater; Global warming; Marine; Meteorology; Ocean circulation; Ocean-atmosphere interaction; Physics of the oceans; Properties; River discharge; River flow; Runoff; Salinity; Sea ice; Sea level; Sea-air exchange processes; Sea-water; Seawater; Water circulation; Wind speed; Winter; Northeast Atlantic; North Atlantic; Baltic Sea; ANE, Baltic Sea; salinity; Century 21st; Scale reduction; Atlantic Ocean; Regional scope; water balance; Climate models; digital simulation; Sea surface temperature; ocean-atmosphere interaction; Forecast model; Ice extent; greenhouse gas; Dynamical climatology; Ocean-atmosphere model; climate modification; sea ice; Ventilation; Forcing; heat transfer; sea level
• ISSN: 0930-7575; 1432-0894
• DOI: 10.1007/s00382-006-0124-x

A regional ocean circulation model was used to project Baltic Sea climate at the end of the twenty-first century. A set of four scenario simulations was performed utilizing two global models and two forcing scenarios. To reduce model biases and to spin up future salinity the so-called Δ-change approach was applied. Using a regional coupled atmosphere-ocean model 30-ear climatological monthly mean changes of atmospheric surface data and river discharge into the Baltic Sea were calculated from previously conducted time slice experiments. These changes were added to reconstructed atmospheric surface fields and runoff for the period 1903-1998. The total freshwater supply (runoff and net precipitation) is projected to increase between 0 and 21%. Due to increased westerlies in winter the annual mean wind speed will be between 2 and 13% larger compared to present climate. Both changes will cause a reduction of the average salinity of the Baltic Sea between 8 and 50%. Although salinity in the entire Baltic might be significantly lower at the end of the twenty-first century, deep water ventilation will very likely only slightly change. The largest change is projected for the secondary maximum of sea water age within the halocline. Further, the average temperature will increase between 1.9 and 3.2°C. The temperature response to atmospheric changes lags several months. Future annual maximum sea ice extent will decrease between 46 and 77% in accordance to earlier studies. However, in contrast to earlier results in the warmest scenario simulation one ice-free winter out of 96 seasons was found. Although wind speed changes are uniform, extreme sea levels may increase more than the mean sea level. In two out of four projections significant changes of 100-year surge heights were found.