Climate change impacts and vulnerability in Europe 2016

Changes in the climate system
few hundred years on average, with previous ones
in 1889 and in the 12th century. It is not currently
possible to tell whether the frequency of these rare
extensive melt events has changed (Nghiem et al.,
2012; Tedesco et al., 2013). Another important
process that may accelerate the loss of ice from the
ice sheets is enhanced submarine melting of glaciers
terminating in the sea. Its importance may be greater
than previously assumed. The process has been
documented for both the Greenland and the Antarctic
ice sheets (Wouters et al., 2015).
East Antarctica had a slightly positive mass balance
of + 14 (– 29 to + 57) billion tonnes per year over the
period 1992–2011, but, overall, the Antarctic ice sheet
has lost on average approximately 70 billion tonnes
of ice per year, as West Antarctica and the Antarctic
Peninsula have lost 65 (39 to 91) and 20 (6 to 34)
billion tonnes per year, respectively. The floating ice
shelves have also become thinner (Paolo et al., 2015).
From 1992 to 2015, the ice loss of the Antarctic ice
sheet has contributed approximately 5 mm (2 to
7 mm) to the global sea level (Clark et al., 2015). All in
all, the ice sheets have contributed to about one-third
of the total sea level rise since the 1990s (Shepherd
et al., 2012; Barletta et al., 2013; Vaughan et al.,
2013; Helm et al., 2014). A recent study of Antarctica
suggests, however, that the snow accumulation has
exceeded the mass loss from ice discharge, leading
to the equivalent of an annual 0.23 mm sea level
depletion between 2003 and 2008 (Zwally et al., 2015).
Projections
All recent studies indicate that the mass loss of the
Greenland ice sheet will increase the global sea level,
with greater radiative forcing leading to greater sea
level rise. Recent studies suggest an upper bound of
16 cm of sea level rise from the Greenland ice sheet
during the 21st century for a high emissions scenario
and somewhat lower values for lower emissions
scenarios (Church et al., 2013; Fürst et al., 2015). One
recent study estimated that the Greenland ice sheet
contribution until the year 3000 will be 1.4, 2.6 and
4.2 m for the emissions scenarios SRES B1, A1B and A2
(with stabilised greenhouse concentrations after 2100),
respectively (Goelzer et al., 2012; Church et al., 2013).
On multi-millennial time scales, the Greenland ice sheet
shows threshold behaviour due to different feedback
mechanisms. If a temperature above the threshold is
maintained for an extended period, the melting of the
Greenland ice sheet could self-amplify, which would
eventually result in near-complete ice loss (equivalent
to a sea level rise of about 7 m). Coupled climate–ice
sheet models with a fixed topography (that do not
consider the feedback between surface mass balance
and the height of the ice sheet) estimate that the global
mean surface air temperature threshold above which
the Greenland ice will completely melt lies between
2 and 4 °C above pre-industrial levels (Rae et al.,
2012; Church et al., 2013; Fettweis, Franco et al., 2013;
Vizcaino et al., 2015). In contrast, a study modelling
Figure 3.11
Cumulative ice mass loss from Greenland and Antarctica
Gigatonnes (Gt)
Greenland
Gigatonnes (Gt)
Antarctica
4 500
4 500
4 000
4 000
3 500
3 500
3 000
3 000
2 500
2 500
2 000
2 000
1 500
1 000
500
0
– 500
1992 1995 2000 2005 2010 2015
Note:
1992
1993
1994
1995
1996
The figure shows the cumulative ice mass loss from Greenland and Antarctica derived as annual averages from more than
100 assessments. The uncertainty interval is estimated from the 90 % confidence intervals (5 to 95 %) of the individual studies.
Source: Shepherd et al., 2015, updated from 2012.
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
1 500
1 000
500
0
– 500
1992 1995 2000 2005 2010 2015
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
Climate change, impacts and vulnerability in Europe 2016 | An indicator-based report
97