Geoscience Reference
In-Depth Information
on the planet and their populations. ENSO is one of the
modes of climate variability discussed by Wanner et al.
[2008] along with the North Atlantic Oscillation, Paci
s
climate, archiving information on past temperatures and
precipitation. Many tropical ice
Glacier ice is one of the most versatile recorders of Earth
'
c
Decadal Oscillation, Atlantic Multidecadal Oscillation, and
the Atlantic meridional overturning circulation.
Another very important component of the tropical circula-
tion is the monsoonal system. The Asian monsoon circula-
tion influences Asia, Africa, and Australia, regions in which
more than 60% of the Earth
fields have provided contin-
uous, annually resolved proxy records of climatic and envi-
ronmental variability preserved in measurable parameters,
especially oxygen and hydrogen isotopic ratios (
18
O and
δ
D) and the net mass balance (accumulation). Ice core re-
cords from Africa, Alaska, Antarctica, Bolivia, China,
Greenland, Peru, Russia, and Indonesia have made it possi-
ble to study atmospheric and oceanic processes linking the
polar regions to the lower latitudes where human activities
are most concentrated. For over 35 years, the Ice Core
Paleoclimate Research Group (ICPRG) at the Ohio State
University
'
s Byrd Polar Research Center has successfully
extracted information on past climatic and environmental
changes from ice cores drilled around the world, often under
very harsh and logistically challenging conditions. Much of
this work has been conducted on tropical mountain glaciers
in the Andes, in the Himalayas, on Kilimanjaro, and most
recently, in Papua, Indonesia. The details of the glaciological
and geophysical studies conducted at each site are available
in over 200 publications published by the ICPRG group
(http://bprc.osu.edu/Icecore/Abstracts/Publications.html).
These low-latitude climate records constitute a critical com-
ponent of the principal objective of our program, the acquisi-
tion of a global array of ice cores that provide high-resolution
climatic and environmental histories that will contribute to
our understanding of the complex interactions within Earth
δ
s population resides [Webster et
al., 1998]. Abrupt variations in monsoon intensity can result
in devastating droughts/floods during very weak/strong
events. At any given time, water evaporated from the world
'
s
oceans stores about a sixth of the solar energy reaching the
surface of the Earth. It is the release of part of this energy that
is responsible for the power and duration of the monsoon
rainy season.
The general warming trend during the twentieth century
and into the twenty-
'
rst century is now well documented.
Scienti
s globally averaged
surface temperature is increasing. The Intergovernmental
Panel on Climate Change (IPCC) [2007] strongly suggests
that human activities are contributing signi
c evidence veri
es that Earth
'
cantly to ob-
served changes in the Earth system. Although not all regions
have warmed, the globally averaged temperature has in-
creased ~0.7°C since 1900 [Hansen et al., 2006]. The best
interpretation of proxy records from borehole temperatures,
stable isotopes from ice cores, tree ring data, etc. suggests
that the decade of the 1990s was the warmest in the last 1800
years [Jones and Mann, 2004; Mann et al., 2009].
On decadal and longer timescales, climate models predict
that greenhouse gas-induced warming will cause tempera-
tures to rise faster at higher elevations and that vertical
ampli
'
s
climate system.
Because tropical glaciers often produce continuous, high-
resolution records of climate, ice cores from these glaciers
have been valuable in the study of past variations, particularly
those of an abrupt (annual to decadal) nature. Additionally,
ice cores drilled through ice sheets and ice caps also provide
information on phenomena and events that drive climate
change, such as volcanic activity, solar variations, vegetation
changes, and greenhouse gas concentrations. Tropical gla-
ciers are currently responding to climate changes that can be
de
cation will be greatest in the tropics due to upper
tropospheric humidity and water vapor feedback [IPCC,
2007, chapter 8, p. 602]. This is not surprising given that
37% of the warm tropical ocean surface water is located
between 20°N and 20°S latitude. Results from general circu-
lation models indicate that water vapor provides the largest
positive radiative feedback and that it alone roughly doubles
the warming in response to forcing such as from greenhouse
gas increase. As a result of this forcing, the projected changes
in mean annual free-air temperatures between 1990 and 1999
and 2090 to 2099, using CO
2
levels from IPCC scenario A2,
shows twice as much warming in the higher elevations
(middle to upper troposphere) in the tropics than is predicted
at Earth
the climate
system is forced to cross some threshold, triggering a transi-
tion to a new state at a rate determined by the climate system
itself and faster than the cause
ned as abrupt, e.g., the condition when
“
takes place so rapidly
and unexpectedly that human or natural systems have trouble
adapting to it
”
[National Research Council, 2002, p. 14].
Evidence for abrupt climate changes, particularly those that
have occurred during the Holocene, is often captured by at
least some of the physical (e.g., insoluble dust or recon-
structed accumulation) or chemical (e.g., stable isotopes of
oxygen) time series of these continuous records. Here present
and past climate changes are discussed along with their im-
pacts on tropical mountain glaciers, and two major abrupt
”
and
“
is surface [Bradley et al., 2006]. Moreover, it is
expected that some high-elevation tropical glaciers may al-
ready be responding to these enhanced temperatures, which
may well account for the accelerating rate of glacier loss at
some of these sites [Thompson et al., 2006a; Coudrain et al.,
2005].
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