Snow, Ice, Avalanches, and Glaciers - Mountain Geography: Physical and Human Dimensions - page 190

at one time or another since 1946” (NSIDC 2008). The most striking fact about glacial
mass balance behavior in the last century has been a widespread glacial retreat (Figs.
4.33, 4.34, and 4.35). There have been short cooling periods with glacial advance, as
in the 1920s (Hoinkes 1968) and from the 1940s through the 1960s (Meier 1965: 803),
but since the late 1900s and early 2000s, global temperatures have continued to rise,
and most glaciers continue to shrink (Charlesworth 1957; Flint 1971; Leggett 1990;
Dyurgerov and Meier 1997a, 1997b; Haeberli et al. 1998; Ding et al. 2006; Barry and
Gan 2011). The NSIDC report continues, “. . . we only have a continuous record from
about 40 glaciers since the early 1960s. These results indicate that, in most regions
of the world, glaciers are shrinking in mass. For the period 1961-2003 'small' glaciers
lost approximately 7 meters in thickness, or the equivalent of more than 4,000 cubic
kilometers of water. The Global Glacier Mass Balance graph [Fig. 4.35] contains data
for average global mass balance for each year from 1961 to 2003 as well as the plot
of the cumulative change in mass balance, expressed in cubic kilometers of water, for
this period” (NSIDC 2008). Especially alarming is the rate of loss of tropical glaciers
(Thompson 2001; Thompson et al. 2003).
Climatic variations and glacial fluctuations such as this are the norm rather than the
exception over long periods of time. It was formerly thought that the major ice age ad-
vances ( stadials ) had each lasted about 100,000 years, separated by somewhat longer
interglacials ( interstadials ) with more stable warmer and drier climates. However, it
is now believed that there were more frequent stadial and inter-stadial periods, each
lasting only 10,000 to 30,000 years (Emiliani 1972; Woillard 1978). The last major sta-
dial ended about 10,000-12,000 years ago, and we are now in an interglacial period.
Shorter-term climatic fluctuations have continued to occur, superimposed on these lar-
ger trends. There is abundant evidence for glacial oscillations on time scales of hun-
dreds to thousands of years (Benn and Evans 2010; Barry and Gan 2011) and, in some
cases, even decades (Nolan 2003). For example, the final melting of the continental ice
was followed by a distinctly warm and dry period, known as the Thermal Maximum
or hypsithermal, which lasted from 4,000 to 10,000 years ago (Deevey and Flint 1957;
Yoshino 2005). The next major change was a widespread readvance of mountain gla-
ciers 2,000 to 4,000 years ago (Denton and Karlen 1973). Subsequent climatic fluctu-
ations, most notably a warming trend about 1,200 to 800 years ago, were followed by
a period of glacial advance known as the Little Ice Age that occurred between the six-
teenth and nineteenth centuries (Grove 1988, 2001; Matthews and Briffa 2005; Solom-
ina et al. 2008). Glacial advance during this period did considerable damage to farm-
land and villages in the Alps and the mountains of Norway. In Iceland, the situation
was compounded by a series of major volcanic eruptions, so that total evacuation of
the entire population was seriously considered by the Danish king (Ives 2007). Dutch
Masters paintings show people skating on the often frozen canals of Holland (Grove
1972; Messerli et al. 1978), and there are reports of ice parties on the Thames River in
England (Ives 2007).
The period of modern glacial retreat witnessed during the twentieth and twenty-
first centuries apparently reflects warming and amelioration of conditions following the
Little Ice Age. While these temporal generalizations apply to most high mountains on
the broad scale, recent evidence reinforces the idea that mountain glaciation is often
asynchronous in different mountain ranges, even though they may be relatively close