The project aims at improving our understanding of the magnitude and spatial structure of Holocene climate variability and its causes, by undertaking transient simulations (experiments) with a state-of-the-art, coupled atmosphere-ocean sea ice General Circulation Model (GCM) ECHO-G for the mid-Holocene period 6.5 ka BP - 4.5 ka BP.
These experiments can be tested for consistency with proxy-based climate reconstructions, and will provide improved estimates for pre-industrial climate variability during the Holocene, which will help to assess with higher confidence how unusual the climate changes since the beginning of the twentieth century are. It also can be analysed for the effects of varying forcing factors. Moreover, as GCMs are the main tool for estimating the sensitivity of future climate to changing atmospheric concentrations of greenhouse gases, but there is still a high level of uncertainty about how realistic GCMs represent the climate, there is a need for long simulations accompanied by consistency tests with proxy data for model validation.
MIDHOL will focus on the mid-Holocene because PROSIMUL and SALSA have produced several results and hypotheses related to the climate evolution during this period, and because standard fully coupled AOGCM climate simulations for the late Holocene, but not for earlier periods, are already available or underway.
Mid-Holocene climate information analysed within PROSIMUL, SALSA and other studies indicates for instance changes in the location of the Southern Hemisphere Westerlies, links between mid-Holocene droughts in the central US and sea surface temperatures around Iceland, and a strong relationship between climate variability recorded in laminated sediments in the Holzmaar (Germany) and North Atlantic Deep Water Formation. A transient coupled atmosphere-ocean sea ice GCM simulation provides an excellent way of examining the climate hypotheses advanced by these studies.