Geoscience Reference
In-Depth Information
Abrupt Climate Change: A Paleoclimate Perspective
From the World
'
s Highest Mountains
Lonnie G. Thompson
Byrd Polar Research Center, School of Earth Sciences, Ohio State University, Columbus, Ohio, USA
fields, along with
other proxy data, provide two primary lines of evidence for past and present abrupt
climate change. First, there is strong evidence from paleoclimate records from
within and around these glaciers for two widespread and spatially coherent abrupt
events during the Holocene: a major isotopic excursion centered on ~5.2 ka B.P.
marks the transition from early Holocene warmth to cooler conditions, and a major
dust increase occurs between 4.0 and 4.5 ka B.P. Both of these events were
concurrent with structural changes in early civilizations. Second, the continuing
retreat of most midlatitude to low-latitude glaciers, many having persisted for
millennia, signals a recent and abrupt change in Earth
Ice core records recovered from high-elevation, low-latitude ice
'
s climate system. High-
18
O (temperature proxy) demonstrate
that the current warming at high elevations in the middle to lower latitudes is
unprecedented for at least the last two millennia, even though they suggest that the
early Holocene was much warmer at many sites. The remarkable similarity between
changes in the highland and coastal cultures of Peru and climate variability,
especially with regard to precipitation, implies a strong connection between pre-
historic human activities and climate in this region. Well-documented ice loss on
Quelccaya in the Andes, Naimona
resolution ice core stratigraphic records of
δ
nyi in the Himalayas, and Kilimanjaro in eastern
Africa paint a grim future for recovery of tropical glacier histories. The current
melting of high-altitude, low-latitude ice
'
fields is consistent with model predictions
for a vertical ampli
cation of temperature in the tropics.
1. INTRODUCTION
oceanic circulations. Most of the meteorological and climatic
events and perturbations affecting Earth
'
s surface originate
in or are amplified by ocean/atmosphere interactions in trop-
ical latitudes. The tropics are Earth
'
s
“
heat engine,
”
where
the warmest atmospheric and sea surface temperatures
(SSTs) occur. The energy associated with these warm tem-
peratures gives rise to intense convective precipitation and is
crucial for the evolution of phenomena such as the El Ni
ñ
o
-
Southern Oscillation (ENSO), the monsoonal systems of
Asia and Africa, and, on shorter time scales, hurricanes and
other tropical disturbances that distribute tropical energy
(heat) poleward. ENSO has strong impacts on meteorologi-
cal phenomena that directly or indirectly affect most regions
Fifty percent of Earth
'
s surface area lies between 30°N and
30°S, which is defined as the geographic tropics. This region
is of immense societal importance as it is home to 70% of the
world
'
s ~7 billion people. It also receives and transmits much
of the thermal energy that drives Earth
'
s atmospheric and
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