Page 253 - Earth's Climate Past and Future

CHAPTER 13

Climate During and

Since the Last

Deglaciation

Earth was transformed following the last glacial maximum. The melting ice
sheets sent enough water to the ocean to raise global sea level by 110–125 m.
The rising ocean submerged links between continents and islands and it
flooded basins that had earlier been cut off from the sea. Meltwater lakes
formed in bedrock depressions left by the retreating ice. Ice lobes dammed
these lakes but were periodically breached, sending catastrophic floods across
the land. Forests and tundra moved north to occupy broad regions abandoned
by the ice, in some regions penetrating beyond their present limits before
retreating in recent millennia. Tropical monsoons strengthened until 10,000
years ago and then weakened.
Abundant, well-dated records permit testing of two theories proposed as
explanations of these changes: the Milankovitch theory that insolation con-
trols ice sheets and the Kutzbach theory that insolation controls tropical mon-
soons. In general, the data confirm both theories: rising summer insolation in
the northern hemisphere initiated melting of high-latitude ice sheets and
strengthened tropical monsoons. Subsequent weakening of monsoons and
cooling of high northern latitudes during the last 7000 years are consistent
with decreasing summer insolation.