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JJ. Haapala et al. 
Fig. 8.1 Maximum ice-cover 
extent in the Baltic Sea (MIB), 
1720-2012. The dashed bars 
represent the error range of the 
early estimates. The 30-year 
moving average is indicated by 
two lines representing the error 
range early in the series, 
converging into one line when 
high-quality data became 
available 
Fig. 8.2 Mean annual maximum 
sea ice extent (blue), 2-m air 
temperature (coloured isolines) 
and 10-m wind vectors over the 
Baltic Sea region during two 
phases of the North Atlantic 
Oscillation: a negative phase 
(NAO < -0.5) and a positive 
phase (NAO > +0.5) (redrawn 
from Vihma and Haapala 2009) 
U_geo,T_air and MIB in NAO- years 
U_geo,T_air and MIB in NA0+ years 
towards ice-free winters. Major changes have occurred in the 
offshore area of the western Baltic Sea and east of Bornholm 
Island, with the lowest frequency of ice occurrence observed 
in the past 30 years. There has been a concomitant decrease 
in the frequency of ‘difficult’ ice conditions (coverage > 7/10 
and thickness > 10 cm). 
Fig. 8.3 The maximum extent of Maximum annual sea-ice extent in the Baltic 
1900 1920 1940 1960 1980 2000 
Years