The Oligocene to the Quaternary: climate and biology - Climate Change: Biological and Human Aspects - page 153

cooling and inferred decreased vegetation productivity were probably responsible for
its disappearance from this region. The cave bear survived significantly later else-
where, for example in southern or eastern Europe. This point is important for two
reasons. First, climate change extinctions are often local and not global. Secondly,
the Quaternary ice age has seen several glacial cool periods interspersed with briefer
warmer interglacials (such as the Holocene one we are now in). This in turn raises
the question as to why some species died out at the LGM and not previous ones.
As mentioned when discussing mammoths (see section 4.3), the new factor in some
parts of the world in the LGM was that of the spread of early humans.
The sea-level rise and flooding of the Beringian Russian-Alaskan land bridge took
place between the LGM and the early parts of our current (Holocene) interglacial.
It is known that some now-extinct Pleistocene fauna survived well into our cur-
rent Holocene interglacial. For example, mammoths ( Mammuthus spp.) survived on
St. Paul Island as late as 7900 years ago and Wrangel Island 3700 years ago, which is
well after the end of the last glacial. Conversely, mammoths that were less isolated on
the Californian Channel Islands became extinct far earlier, around the time of human
arrival c .11 000 years ago (Guthrie, 2004). The relationship between this mammoth
extinction and human arrival is thought to be causal. Had the Beringian islands been
much larger, so as to enable larger populations (and hence reduced inbreeding), then it
is possible that mammoths might have survived for longer in the absence of humans,
perhaps even to the present day. (Beringia should not be considered as just a land
bridge but, for reasons alluded to above, also a land area where many characteristic
Pleistocene species and communities evolved.)
This prehistoric extinction demonstrates how stress from both climate change and
from humans affects species: a negative synergy of much relevance to current and
future climate ecology. The story of this megafaunal extinction spans the LGM, and so
is part of this section's discussion on the last glacial, but it also continued on through
the glacial-interglacial transition and into the Holocene. So we will return to this
topic in sections 4.6.3 and 4.6.4 on the Holocene.

4.6 Interglacialsandthepresentclimate

4.6.1 Previousinterglacials

We are currently in an interglacial, the Holocene interglacial, but there have been
several other Quaternary interglacials. The last one before ours was the Eemian
(sometimes known as the Sangamon) interglacial some 125 000-115 000 years ago.
It began just like our current interglacial with a geologically short period (around a
century or two) of rapid warming. Indeed, the warming may well have been faster
due to changes in ocean circulation but tempered due to the massive ice sheets that
took time to melt following the previous glacial's maximum. What is known is that
the temperature early in the Eemian interglacial was a degree or so warmer than at
present. This lasted for a few centuries before cooling to present-day temperatures.
Also during the last interglacial period, 'North Atlantic Deep Water' was 0.4 0.2 ◦ C

warmer than today, whereas 'Antarctic Bottom Water' temperatures were unchanged.

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