Page 233 - Earth's Climate Past and Future
P. 233
CHAPTER 12
Last Glacial Maximum
When the most recent of the ∼100,000-year glacial oscillations culminated
21,000 years ago, most of Earth’s surface was very different from its current
appearance. Ice sheets 2 or more km high covered Canada, the northern United
States, northern Europe, and parts of Eurasia. Global sea level was 110–125 m
lower, joining modern islands between Asia and Australia and connecting
Britain to mainland Europe. South of the ice sheets, conditions were cold and
windy, with dust blowing in many areas. The modern forests of North America,
Europe, and Asia were regions of tundra or grasslands, and lower levels of
atmospheric CO and CH caused cooling and drying across the tropics and the
2 4
southern hemisphere.
In this chapter we focus on aspects of this glacial world such as the extent
and thickness of the ice sheets and the debris they produced. Then we explore
how changes in the distribution of life forms, especially land vegetation and
ocean plankton, allow us to test climate simulations run on general circulation
models. Finally, we examine a controversy that has implications for future
changes in climate: How cold were the tropics at the last glacial maximum?
