Simulations using the CCSM3 comprehensive AOGCM: Mechanisms of abrupt climate change and natural variability during the last centuries

• Main Author: Renold, Manuel
• Other Authors: Stocker, T. F.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2007
• Subjects: 530 Physics; Antarc*; Antarctica; Greenland
• Online Access: https://boris.unibe.ch/192513/1/renold07phd.pdf; https://boris.unibe.ch/192513/

Proxy evidence from many tracers such as ice cores in Greenland and Antarctica reveal that the earth’s climate has changed several times in the past. The last 700,000 years are punctuated by transitions between glacial and interglacial periods. Different periods have been detected and linked to changes in the earth’s orbit, eccentricity, axial tilt, and precession. The last of such a cycle ended approximately ten thousand years ago. The global climate moved from a glacial to a much warmer climate. Since then, the climate has been in a remarkably stable state. Throughout the entire Holocene only small fluctuations of the climate such as the Little Ice Age, the Medieval Warm Period or the 8.2 ka event are known. To assess the predictability of future climate changes it is of crucial importance to have a profound knowledge of past climate history and the mechanisms controlling these changes naturally. The climate changes of the past leave their traces in many proxies, such as marine and lake sediments, corals, ice cores, and glaciers. Climate records reflect local as well as large-scale variability of the climate. Climate models represent an excellent instrument to combine these proxies of different time scales and spatial distributions to investigate past climate history and the related mechanisms. The power of today’s computers permits the use of complex climate models simulating numerous physical and chemical processes. In conjunction with supercomputers and PC-clusters, simulations of hundred to thousand model years are possible to calculate, even with complex Atmosphere-Ocean-General-Circulation models (AOGCM). In contrast to climate models with reduced complexity, the AOGCM simulate many modes of internal variability. This is a great advantage, because it allows the investigation of atmospheric modes. In this thesis the AOGCM Community Climate System Model (CCSM) was used to carry out two types of experiments. One addresses Dansgaard-Oeschger/Heinrich events, and a second is focused on simulations of the past ...