The Oligocene to the Quaternary: climate and biology - Climate Change: Biological and Human Aspects - page 163

Cool, drier interglacial Warm, wetter interglacial

Warmth maintained

Algal bloom promoted,
drawing down of carbon dioxide

More ocean
evaporation

More dust

Climatic effect
(forcing)

Less rain More rain

Less algal drawdown
of carbon dioxide

More dust washed
out over land

Less ocean evaporation

Less dust fertilising algal growth

Coolness maintained

Fig. 4.13 Climate-dustinteractionscombinetotendtomaintaineitheracool(glacial)orawarm(interglacial)mode.

ThisisjustoneoftheprocessestendingtokeeptheEarthinoneofanumberofclimatestates.

filled and Britain became an island only as recently as about 7000 years ago, some
4000 years after the end of the last glacial. From this we can see that the approximate
average rate of sea-level rise over this time was a little more than half a metre a
century. Having said this it is important to note that this is an average rate and there
were times between the LGM and 7000 years ago when sea-level rise was faster (see
Chapter 6), and others when it was slower.

4.6.3 TheHolocene(11700yearsago-theIndustrialRevolution)

About 11 600 years ago the Earth finally emerged from the last glacial into a warmer
climate mode that has lasted until the present. (Although the official date for the
commencement of the Holocene is 11 700 years ago, based on key - Global Standard
Section and Point - geological strata.) Average snowlines around the planet (where
latitudinally climate allowed this) rose around 900 m after the last glacial maximum
(LGM). On the basis of today's temperatures this suggests an atmospheric warming
of about 5 ◦ C and of the tropical sea surface of some 3 ◦ C. Of course, the huge amount
of ice left over from the last glacial did not disappear as quickly as the Milankovitch-
forced climate had changed. It took some 3000 years for the Fennoscandian sheet
over northern Europe and Russia to largely disappear and over 5000 years for the
North American Laurentide ice sheet to collapse. This slower collapse may have been
in part because of the vagaries of the climate due to atmospheric circulation but was
probably more connected with the proximity of the higher latitude Greenland ice
sheet, which is still with us today, and of course which provides us with valuable
palaeoclimatic records from its ice cores.
The melting of the ice sheets themselves continued to have an effect on the northern
hemisphere's climate around 8200 years ago. This is sometimes known as the 8.2
kiloyear event. It is thought (Barber et al., 1999) that a pulse of meltwater from