Environmental Engineering Reference
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process—for example, the development of a cold deep-water circulation,
separate development of the East and West Antarctic Ice Sheets, initiation of
Arctic Ocean ice cover and glaciation on Greenland, and onset of signifi cant
mid-latitude Northern Hemisphere glaciation.
When compared with the long-term paleoclimate record, the Cretaceous-
Tertiary (K-T) extinction stands out as somewhat different from the other
extinctions (Crowley and North 1988). The background oxygen isotope
record is relatively stable over a 10 to 15 Ma interval bracketing the event
(Fig. 2a), so there is no step-function change in the climate. There was a
general fall in sea level between the late Cretaceous and early Tertiary
(Miller et al. 2003), but with little geological evidence that it may have been
associated with an ice-growth event (Miller et al. 2008). The effect of abrupt
climate change on organisms can be evaluated in more detail by comparing
the oxygen isotope record of the last 100 Ma (Fig. 2a) with extinction events
in marine invertebrates (Regan et al. 2001) over the same interval (Fig. 2b).
First three of the extinction events coincide to some degree with the three
major steps in the evolution of Cenozoic climate: the onset of mid-latitude
Northern Hemisphere glaciation at about 2.4 to 3.0 Ma (Schaefer et al. 2006);
expansion of ice on Antarctica between about 10 and 14 Ma (Shevenell et al.
2004); and major cooling between about 31 and 40 Ma (Bond et al. 1993).
A fourth extinction event at about 90 Ma coincides with a major
environmental change not manifested in the oxygen isotope record: an ocean
anoxic event (Leckie et al. 2002) that correlates with the highest sea level
of the last 200 Ma (Miller et al. 2005) and with an abrupt change in carbon
isotopes in pelagic carbonates (Hesselbo et al. 2007). Changes in organic
carbon burial may have signifi cantly affected atmospheric pCO 2 levels at
this time (Royer et al. 2004). This last event is therefore also a candidate
for an abrupt environmental change due to slowly changing boundary
conditions. Some of the second-order trends in the oxygen isotope record
also correlate with smaller extinction events (Wing et al. 2005).
However, the 18 O event at 36 Ma (Fig. 2a) represents only one of at least
three stages of climate change that resulted in an overall transition from the
warm climates of the Early Tertiary to the cool climates of the Late Tertiary:
Late Eocene cooling (36 to 40 Ma), abrupt bottom water cooling with some
ice growth at about 36 Ma, and a major sea level fall and presumed ice
growth event at about 31 Ma (Crowley and North 1988).
A different time-scale observation: the decadal climate variability
The effects of anthropogenically forced climate change are expected to
continue through the twenty-fi rst century and beyond. However, on a
timescale of a few years to a few decades ahead, future regional changes
in weather patterns and climate, and the corresponding impacts, will also
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