Late Quaternary Climate Fluctuations and Their Causes: A Brief Review

Abstract

Toward the Cenozoic, global climate tended to cool gradually and the coldest period was found in the late Quaternary. In particular, the last glacial maximum (LGM) is known to have occurred at 21,000 years before present (BP). During the LGM the global-mean sea surface temperature decreased by 5？°C and the hydrological cycle was weakened with a drier climate. The North Atlantic Deep Water production was markedly reduced in the glacial period and the all ocean basins were filled with the water originated from the Southern Ocean. The glacial period lasted until 18,000 yr BP in the southern hemisphere and 14,000 yr BP in the northern hemisphere, respectively, and then deglaciation abruptly began. In the northern hemisphere, the deglaciation led to the huge melting of ice sheet from North America and discharge to the northern North Atlantic, resulting in the shut-down of the North Atlantic Overturning. The consequent cold-climate event, called Younger Dryas, was happened at 11,000 yr BP. At the beginning of the Holocene, the climate had warmed up due to the increase in solar radiation associated with the change in earth's orbital parameters. The peak warmth occurred during the early- to the mid-Holocene (10,000-6,000 yr BP) when surface temperature was higher by 1-4？°C regionally and the climate was overall wetter than present. In particular, an increased summer solar radiation in the northern hemisphere enhanced summer monsoon, resulting in the increase in precipitation over most Asia. Since the mid-Holocene, the climate began to cool gradually up to the preindustrial time as the Neoglacial period and especially the coldest climate (Little Ice Age) was recorded between AD 1,100 and 1,800 years. Since the industrial revolution, the temperature has markedly increased up to now presumably associated with the increase in greenhouse gas concentration. The degree of recent warming is unprecedented at least for the past 10,000 years. The paleoclimate proxy records have shown climate change pattern and variability, but they are limited in revealing how climate was operated in different climate background. Thus, a hierarchy of numerical models has been used in investigating paleoclimate events, especially the LGM and Holocene periods. To help predict a future climate change correctly, both paleoclimate proxy and numerical model studies must be performed in parallel.