The East Asian Summer Monsoon : A comparison of present, Holocene and Eemian climate

The East Asian Summer Monsoon (EASM) is a major component in Asian climate. It is largely driven by climatic factors such as humidity, solar insolation and temperature. For at least 50 years the EASM has been studied extensively by scientists regarding its current strength. Models have been recreating past monsoon intensity as well as attempted to predict future intensity. As the monsoon undergoes changes, the climatic shifts responsible for them leave various traces behind; geochemical as well as biological, and these have been preserved and recorded in various locales on the planet. The most significant climatic change is the variation between glacial and interglacial periods which have been alternating for the last 2.6 million years and the EASM has changed in tune with the climate during this time. The EASM follows the δ18O-record in speleothems found in Eastern Asia as well as in ice cores from Greenland. Various geochemical and biological tracers seem to reflect these fluctuations in climate locally as well as globally over a 200 kyr period. The current intensity of the EASM seems to be one of decreasing strength, a phase that has persisted since the Holocene climatic optimum 8.5 kyr ago. Recently however a decrease in the East Asian Winter Monsoon has been confirmed, indicating an increase in EASM intensity. During the Holocene the EASM reached peak intensity during the Holocene climatic optimum but has fluctuated largely in tune with solar insolation. This is also true for the Eemian period although some events such as the mid-Eemian cooling show that factors other than solar insolation regulate monsoon intensity over large time periods. The future of the EASM seems to be one of increased strength due to climate change and models predict both increased wind speeds and an increasing occurrence of extreme precipitation despite decreasing solar insolation