The coldest winter in the Baltic Sea region
 for 30 years, but where is sea ice 
in winter 2009/10?

Text based on a posting by Arnd Bernaerts at:
08 March 2010;
short version

The winter 2009/10 was the coldest since long. All over Northern Europe the temperatures had been permanently below the freezing point since the Climate Summit in Copenhagen from 07-18 December 2009. During a cold winter the Baltic Sea reacts with a corresponding icing, but not this winter. Even in February the sea ice was modest. Attention got the Baltic Sea only few days ago, when new report  informed the world that about 50 vessels got stuck in ice between Stockholm and Helsinki around the 4th of March 2010, while the Finnish Ice Service informed of an sea ice increase on the 8th of March (Fig. 4 & 5). Have this circumstances a reason that science in the 21st Century should be able to explain? A comparison between this winter and the first war winter 1939/40 would not be a harm.
                                        Fig. 1 (Source: FMI – Baltic Sea Portal)

Although  a detailed analysis is pending, there is little doubt that winter had been the coldest for many decades, stretching from England, to Finland, and NE Russia. In the middle of this cold area the Baltic Sea from the Kattegat to the Bay of Bothnia. Permanent minus temperature and the forming of sea ice are closely connected. If this assumption is correct, than the extent of sea ice should have reached a level as at the end of the 1980s, when there had been a corresponding cold winter, and a high level of sea ice.  From the caver than the current ice cover is far away. The last full cover occurred in the winters 1939/40, 1941/42 and 1946/47, and the second war winter 1940/41 a similar high coverage has a the highest sea ice level in the 1980s (see: Fig, 1).

The sea ice conditions in February  & March 2009 (Source. FMI)

The maximum ice area for
the winter 2009/10 according FMI


Fig. 2, Sea Ice 17. Feb. 2010

Fig. 3; 06 March2010 (FMI, No.98)



Eislage am 01. März 2010 (Fig.4)





Eislage am 08. März 2010 (Fig. 5)

Can the modest ice cover until mid February, and the late increase during the first days of March in any way be attributed to the extensive shipping activities in the Baltic Sea?  

Some consideration on two ice winters:  
1939/40 versus  2009/10 

The winters during the 1930s had been the warmest since the 19th Century, as well indicated in by the winter temperature data (DJF) from Stockholm (Fig. 6). But from winter 1938/39 to the first war winter 1939/40 the data crashed, producing a full Baltic Sea ice cover for the first time after six decades.  It followed a series of icing, that had not happened since for more than 100 years (Fig. 7). Suddenly for three winters the Little Ice Age was back in Europe (see Fig. 6). 


Fig.6  DJF-Temp, Stockholm

Fig. 7, Highest Sea Ice cover 



To identify the reason one should not look for distant events or cycles (.e.g. El Nino , or NAO) but consider the role and impact huge naval armadas and activities have had on the heat content of the regional seas. Since the 1st of September they criss-crossed the waters, shelled, mined, and bombed the enemy. The heat stored during the summer is quickly released, with the presumably inevitable consequence that General Frost could take reign very early, long, and severe.  


 A corresponding mechanism could have influenced the sea ice conditions during the last winter. Of course the naval farce are not the issue nowadays, but shipping. About 2000 sizable ships a permanently navigating the Baltic Sea, which means that this armada may turn the entire sea surface level over a depth to 7-10 meters in about twice a months (Fig. 8), with the consequence that:

  • During summer more heat is induced into the Baltic Sea.
  • In autumn the loss of heat is higher than without shipping
  • During the winter season (January and February) intensive shipping ensures a warmer sea surface by moving deeper and warmer water to the surface, which prevents, or delays the forming of sea ice. 
To take stock of the reasoning it would explain the temperature increase over several decades, and the astonishing sea ice difference between pervious cold winters and the last winter.