Using climate models to unraveling past conditions during Earth's history and its relevance to Climate Change

During the mid 1970s global climate models were used to examine climate conditions of the past. Initially these early studies considered how external changes would influence the climate system and the ocean was considered as a fixed boundary condition. By the early 1980s the ocean evolved from a fixed boundary condition, to one acting solely as a moisture source and finally to considering the thermodynamic and dynamic states of the ocean. At the same time, the role of internal boundary condition (greenhouse gas concentrations, continental configuration, rotation rate, ice-sheets) as a means for understanding past climate were being taken into account. Many of the early studies used the National Center for Atmospheric Research (NCAR) community climate model (CCM) as the model of choice for studying paleoclimates. Today climate models are capable of examining the full climate system (atmosphere, ocean, cryosphere, biosphere, ocean) with paleoclimate modelers examining past climates and also attempting to simulate the last 500 years. If these simulations agree with the observed proxy record, then it may be possible to bracket the natural climate variability prior to the industrial revolution in climate models. Moreover, these types of simulation allow for the analysis of interannual to centennial variability. Consequently, the ability to correctly simulate past climates can only increase our confidence in simulating future climate change caused by anthropogenic greenhouse forcing.