Mountain Climate - Mountain Geography: Physical and Human Dimensions - page 130

last century (Kaab et al. 2002; Kaser et al. 2004; Barry 2008). Small glaciers in many
mountains have already disappeared and more are feared to become extinct if global
warming trends continue (Dyurgerov 2005; Zemp et al. 2006).
As a result of temperature changes, glacial recession, and changing snowpacks,
downstream runoff characteristics (i.e., seasonality and magnitude) may be altered ap-
preciably over the next several decades (Adam et al. 2009; Stewart 2009; Clow 2010;
Kohler et al. 2010; Xie et al. 2010; Kaltenborn et al. 2010). If glaciers entirely disappear
from mountains, then melt-season, especially late-melt-season, discharge will decrease
substantially (Fig. 3.22). Glaciers are estimated to provide 6-30 percent of annual runoff
in some rivers (Bach 2002). Changes to mountain hydrology will have significant con-
sequences not only in the mountains themselves, but also in the populated lowland re-
gions that depend on the runoff for domestic, agricultural, energy, and industrial uses
(Beniston 2006; Kohler et al. 2010). Even climate changes in nonglaciated, low moun-
tains can have a significant impact on municipal water supplies (Frei et al. 2002; Mote
et al. 2003). Runoff from glacier melt is responsible for a substantial component of the
current rise in eustatic sea level (Dyurgerov and Meier 1997; Raper and Braithwaite
2006).
Climate change is considered a major threat to mountain ecosystems (McCarty 2001;
Grace et al. 2002; Parmesan and Yohe 2003; Root et al. 2003; Beniston 2006; Nogués-
Bravo et al. 2008; Kohler et al. 2010). Since many organisms living in mountains sur-
vive near their tolerance range for climatic conditions, even minor climatic changes
could have a significant impact on alpine ecosystems (Grabherr et al. 1994; Thuiller
2004; Erschbamer 2007). Vegetation zones will migrate altitudinally and latitudinally
in response to warming temperatures, possibly eliminating some biomes, although the
adaptations will likely be more complex (Thuiller 2004; Colwell et al. 2008). Because
mountain tops are smaller than their bases, biomes shifting upslope will occupy smaller
and more fragmented areas, reducing populations and increasing genetic and environ-
mental pressures (Thuiller 2004; Beniston 2006). However, because different species
respond uniquely to environmental pressures, ecological communities may disassemble
as individual species shift their ranges in different directions and at different rates (Col-
well et al. 2008). Migrants and hibernators may experience problems as a consequence
of these changes in phenology, and may no longer be stimulated by the same environ-
mental cues (Inouye et al. 2000). Complex topography will result in habitat fragmenta-
tion and the creation of barriers to migration, making it difficult for some species to ad-
apt and allowing others, often invasive species, to expand their range. There is a chance
that the quaking aspen ( Populus tremuloides ), Engleman spruce ( Picea engle-mannii ),
and lodgepole pine ( Pinus contorta ) of the western North American mountains might
not survive under projected climate changes (Hansen et al. 2001; Coops and Waring
2011).
With warmer temperatures and elevated CO 2 concentrations, forests may begin
growing earlier in the spring and throughout the growing season; however, changes in
moisture could slow growth (McKenzie et al. 2001). Treelines in many mountainous re-
gions have been responding to recent temperature changes by migrating upslope (Kull-
man and Kjallgren 2000; Pallatt et al. 2000; Klasner and Fagre 2002; Grace et al. 2002;
Graumlich et al. 2005). However, in some topographic settings cold air drainage will
equal or exceed the warming rate, potentially providing refugia for some speices (Daly