Climate change impacts and vulnerability in Europe 2016

Changes in the climate system
Figure 3.8
Arctic sea ice extent
Million km 2
18
16
14
12
10
8
6
4
2
0
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
2011
2013
2015
March
March trend
September
September trend
Note:
Source:
Trend lines and observation points for March (the month of maximum sea ice extent) and September (the month of minimum sea ice
extent) are indicated. This figure does not reflect the reduction of sea ice thickness, which has also been declining over the same period.
EUMETSAT Satellite Application Facility on Ocean and Sea Ice (OSI SAF) and CryoClim. Data delivered through Copernicus Marine
Environment Monitoring Service.
thicker multi-year floes (Comiso, 2012). A recent
analysis has found that annual mean ice thickness
has decreased from 3.59 m in 1975 to 1.25 m in 2012,
i.e. a 65 % reduction in less than 40 years (Lindsay
and Schweiger, 2015). This supports findings from
calculations of sea ice volume from satellites and an
earlier estimate by the Pan Arctic Ice-Ocean Modeling
and Assimilation System (PIOMAS) ( 44 ), which suggests
that the mean monthly sea ice volume has decreased
by about 3 000 km 3 /decade since 1979 (Schweiger
et al., 2011, updated with PIOMAS data available
online).
Information on sea ice extent in the Baltic Sea goes
back to 1720. The maximum sea ice extent has
displayed a decreasing trend most of the time since
about 1800 (Figure 3.9). The decrease in sea ice
extent appears to have accelerated since the 1980s,
but large interannual variability makes it difficult to
demonstrate this statistically (Haapala et al., 2015).
The frequency of mild ice winters, defined as having
a maximum ice cover of less than 130 000 km 2 , has,
however, increased from seven in 30 years in the
period 1950–1979 to 15 in the period 1986–2015. The
frequency of severe ice winters, defined as having
a maximum ice cover of at least 270 000 km 2 , has
decreased from six to four during the same periods.
Projections
Improving the ability to track the observed rapid
summer-time melting of Arctic sea ice has been a
challenge for modelling (Stroeve et al., 2012), but
observations fall well within the model range in
recent modelling studies (Hezel et al., 2014). All model
projections agree that Arctic sea ice will continue to
shrink and thin. For high greenhouse gas emissions
scenarios, a nearly ice-free Arctic Ocean in September
is likely to occur before mid-century (Figure 3.10)
(Massonnet et al., 2012; Stroeve et al., 2012; Wang and
Overland, 2012; Collins et al., 2013; Overland and Wang,
2013). An extension beyond 2100 suggests that, for the
highest emissions scenario (RCP8.5), the Arctic could
become ice-free year-round before the end of the 22nd
century; on the other hand, a recovery of Arctic sea ice
could become apparent in the 22nd century if stringent
( 44 ) http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly.
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