152 
JJ. Haapala et al. 
70 
E 
о 
60 
</> 
СЛ 
50 
CD 
c 
40 
2* 
О 
30 
‘jz 
t- 
20 
o 
и 
10 
0 
■ 1961-1990(max) ■ 1971-2000(max) ■ 1981-2010( max) 
• 1961-199CH mean) • 1971-2000(mean) • 1981-2010(mean) 
• • , 
• • 
•• 
• • • 
ф CD 
C sz 
c ü 
— со 
о 
</) у 
Ф b 
5 | 
<5 5 
i i 
о £ 
w щ I <Ь Ф m 
12 3 
2: (0 2. аз TD 
0 5 <5 5 0 
ö О CO 
Ф О 0) 
Fig. 8.8 Mean and extreme annual maximum ice thickness (for winters with ice only) on the German Baltic Sea coast within the 30-year periods 
1961-1990, 1971-2000 and 1981-2010 (Schmelzer et al. 2012) 
8.5 Conclusion 
Sea ice conditions in the Baltic Sea have been systematically 
monitored for more than a century. All sea ice-related 
parameters display large interannual variability, but a 
change towards milder ice winters has been observed over 
the past 100 years: in particular, the annual maximum ice 
extent has decreased, and the length of the ice season has 
become shorter. Interannual variability in sea ice conditions 
is principally driven by the large-scale atmospheric circu 
lation. In particular, the winters of strong westerly circula 
tion, that is during positive phases of the NAO, have 
manifested as a minimum ice cover in the Baltic Sea. 
However, a winter without any ice formation in the Baltic 
Sea is far from the present climatology. According to some 
300 years of records of annual maximum sea ice extent, the 
northernmost sub-basin, the Bothnian Bay, has been entirely 
ice-covered even during the mildest winters, and the length 
of the ice season near the coast has been 150 days at a 
minimum. 
In addition to a tendency towards milder winters, the 
occurrence of severe ice winters, when the southern Baltic 
Sea is ice-covered, has also decreased considerably over the 
past 25 years. Although these observations are consistent 
with the changes in global climate, ice season length 
declined to a similar extent during the first half of the 
twentieth cenUtry, when anthropogenically derived green 
house gas emissions are likely to have had almost no impact 
on climate. Long-term changes in the Baltic Sea regions 
have been interpreted as the result of a recovery from the 
‘Little Ice Age’ (Omstedt et al. 2004), but changes in sea ice 
could also be due to shipping. Motivation for sea ice mea 
surements has been the provision of data for shipping, and 
consequently, monitoring sites have typically been located 
near harbours. Ship-induced waves are known to prevent the 
formation of a permanent ice cover in auUimn and also to 
enhance break-up of the ice cover in spring, and so an 
increase in the size of vessels and the intensity of shipping 
activity could also affect local ice conditions. 
Open Access This chapter is distributed under the terms of the Creative 
Commons Attribution Noncommercial License, which permits any 
noncommercial use, distribution, and reproduction in any medium, 
provided the original author(s) and source are credited. 
References 
Alenius P, Seinä A, Launiainen J, Launiainen S (2003) Sea ice and 
related data sets from the Baltic Sea. AICSEX - Metadata Report, 
Meri. Finnish Institute of Marine Research 49:3-13 
BACC Author Team (2008) Assessment of Climate Change for the 
Baltic Sea Basin. Regional Climate Series, Springer-Verlag, Berlin, 
Heidelberg 
Chen D, Li X (2004) Scale-dependent relationship between maximum 
ice extent in the Baltic Sea and atmospheric circulation. Global 
Planet Change 41:275-283 
Girjatowicz J (2011) Ice conditions on the Southern Baltic Sea coast. 
J Cold Reg Eng 25:1-15 
Girjatowicz KP, Kozuchowski К (1999) Variations of thermic and ice 
conditions in the Szczecin Lagoon region. In: Järvet A (ed). Second 
workshop on the Baltic Sea Ice Climate. Dept Geography, Univ 
Tartu 84:69-73 
Haapala J, Leppäranta M (1997) The Baltic Sea ice season in changing 
climate. Boreal Environ Res 2:93-108 
Jaagus J (2006) Trends in sea ice conditions in the Baltic Sea near the 
Estonian coast during the period 1949/1950-2003/2004 and their 
relationship to large-scale atmospheric circulation. Boreal Environ 
Res 11:169-183 
Janssen F (2002) Statistische Analyse mehrjähriger Variabilität der 
Hydrgraphie in Nord- und Ostsee. PhD Thesis, University of 
Hamburg, Germany 
Jevrejeva S (2000) Long-term variability of sea ice and air temperature 
conditions along the Estonian coast. Geophysica, 36:17-30 
Jevrejeva S (2001) Severity of winter seasons in the northern Baltic Sea 
between 1529 and 1990: reconstmction and analysis. Clim Res 
17:55-62 
Jevrejeva S, Drabkin VV, Kostjukov J, Lebedev AA, Leppäranta M, 
Mironov YeU, Schmelzer N, Sztobryn M (2004) Baltic Sea ice 
seasons in the twentieth century. Clim Res 25:217-227 
Jurva R (1937) Über die Eisverhältnisse des Baltischen Meeres an den 
Küsten Finnlands. Finnish Institute of Marine Research 114 
Jurva R (1952) On the variations and changes of freezing in the Baltic 
during the last 120 years. Fennia 75:17-24 
Karvonen J (2012) Operational SAR-based sea ice drift monitoring 
over the Baltic Sea. Ocean Sei 8:473-483 
Koslowski G, Glaser R (1995) Reconstmction of the ice winter severity 
since 1701 in the Western Baltic. Climatic Change 31:79-98