General circulation modelling of Holocene climate variability

Results from a series of Goddard Institute for Space Studies (GISS) General Circulation Models (GCMs) are used to assess climate variability in the pre-anthropogenic Holocene, the interval following the end of the last glacial beginning roughly 11.5 kyr BP. In particular, we focus on the forced aspects of this variability. The principle forcings are orbital, solar, volcanic and events (such as the 8.2 kyr BP event). Land use and greenhouse gases also play a small role. We discuss suitable comparisons to paleo-data and the appropriateness of model experimental design for single and multiple forcing runs using time-slices and transient simulations. As an example, we focus on the response to solar and volcanic forcing in the context of the Maunder Minimum, a cool period of the late 17th century and demonstrate that although (northern) hemispheric mean temperature changes can be reasonably simulated in most models, the details of regional patterns depend more heavily on the included physics. In particular, we highlight the role of the stratosphere as well as the importance of ocean and vegetation feedbacks.