UC San Diego

Following the last glaciation, the climate of the last 11, 600 years (Holocene) has been warmer, wetter, and more stable, fostering development of human agriculture and civilization around the globe. This thesis focuses primarily on the climatic variation of the last 11,600 years based upon an ice core reconstruction of Greenland temperature and atmospheric gases. Then, prior studies of associated impacts on human society are briefly reviewed. This study employs high-precision analyses of argon and nitrogen isotopes in air-bubbles in a central Greenland ice core (GISP2). With a new method to analyze nitrogen and argon isotopes simultaneously and a new algorithm to calculate surface temperature, various climatic changes during the past 11,600 years are revealed. A previously identified abrupt climate change around 8,200 years ago is characterized by an abrupt cooling of 3.3 ± 1.1 ⁰C in less than 20 years with a simultaneous decrease of atmospheric methane concentration. A newly identified abrupt warming of 4 ± 1.5 ⁰C at 11,270 B.P. is found at the end of a cooling known as the Preboreal Oscillation, which was the last large abrupt warming event in the record. This may suggest that the oceanic circulation condition finally reached a warm and stable Holocene mode after this event. The Greenland temperature history of the last 1000 years clearly shows the "Medieval Warm Period" and "Little Ice Age" with persistent multidecadal temperature fluctuations. A strong correlation is observed between Northern Hemisphere temperature and Greenland temperature with a possible lag of Greenland temperature by 20-30 years, suggesting that the two share common causal factors such as volcanic and solar forcing for the last 1000 years. It has been suggested that these climatic events had impacts on past human societies. As the Earth's environment is expected to undergo a substantial change in the future, the past history of climate and society may provide valuable lessons