Environmental Engineering Reference
In-Depth Information
space) interaction with Milankovitch cyclicity to provoke the Quaternary
cycles of glaciation (c. 10ºC change with c. 100,000 year periodicity) that
have persisted for the past 2.5 million years (Crowley and Hyde 2008). The
last glaciation ended 12,000 years ago and Earth is presently in a warm
period. Climatic changes have also occurred at higher frequencies (stadials/
interstadials), but these changes are not necessarily global (Brierley and
Kingsford 2009). In the north Atlantic region, for example, Dansgaard-
Oeschger and Bond events (Bond et al. 1997) occur roughly every 1500 years,
and include the beginning of the Younger Dryas and the Little Ice Age.
Fluctuating ocean circulation and associated greenhouse gas variations are
implicated in these climate oscillations (Schmittner and Galbraith 2008).
The climate history of the early Paleocene is marked by long-term
global warming, beginning in the Late Paleocene (Selandian, ~59 Ma) and
fi nishing in the Early Eocene (Ypresian, ~50 Ma) (Zachos et al. 2001, 2008).
In addition to this long-term warming trend, a short term hypothermal
event (ca 200 kyr) at the Paleocene-Eocene boundary (P-E) known as the
Paleocene-Eocene Thermal Maximum (PETM) had a signifi cant impact
on marine and terrestrial biota (Zachos et al. 2005, Tripati and Elderfi el
2005).
In addition, both the abrupt environmental change and extinction events
may also result from a discontinuous climate response to slowly varying
terrestrial boundary conditions; that is, under certain conditions, instabilities
in the climate system can be triggered by small changes in force (Smith A.
et al. 2001). Theoretical support for the hypothesis of abrupt climate change
is based on climate model results that suggest the presence of multiple
equilibrium climate states for a given level of forcing. Transitions between
states at “critical points” can be rather sudden and can be caused by small
changes in forcing (Crowley and North 1988).
There are some particularly good examples of abrupt climate change
in records from the Quaternary: the terminations of Pleistocene glaciations
(Corliss et al. 1984), the “Younger Dryas” cool oscillation during the last
deglaciation (Brauer et al. 2008), evidence for rapid climate swings in the
interstadial preceding the last glacial maximum (Denton et al. 2010), the
abrupt initiation of glaciation during the early stages of a glacial cycle (Zacos
and Kump 2005), and a relatively abrupt transition in the dominant period
of glaciations during the mid-Pleistocene (Sosdian and Rosenthal 2009).
There is also evidence of signifi cant changes in the evolution of climate
for the last 100 million years (Ma) (Fig. 2a). The long-term trend involves
the evolution of climate from an ice-free earth in the mid-Cretaceous
(100 Ma) to a bipolar glacial state with periodic glacial expansion into
northern mid-latitudes (Poulsen et al. 2001). There have also been signifi cant
increases in aridity during the last 30 Ma (Wolff et al. 2006). Each stage in
the isotopic curve presumably involves one stage in the evolution of this
