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The mid-Holocene (~6000 years ago) is often described as a warm state, or the most recent “climate optimum”, in which dominant features of the global hydrological cycle, such as the North African and Asian monsoon, were amplified. As such, the mid-Holocene has been the focus for paleo-data syntheses since the beginning of the PMIP project and therefore are well documented in terms of temperature, hydrological cycle and land surface type. Some long standing model-data disagreement are echoing preoccupations for future climate change, such as the systematic underestimation of the northward penetration of the African monsoon rainfall onto the continent compared to available records for the Mid-Holocene.
The reference experiment to which the mid-Holocene is compared to is the pre-industrial control, which is part of the DECK.
For the mid-Holocene, our proposed experimental set-up for PMIP-CMIP6 is unchanged compared to the PMIP3-CMIP5 set-up:
The main forcing is the insolation , and the astronomical parameters must be set to:
eccentricity = 0.018682
obliquity = 24.105°
perihelion-180° = 0.87°
solar constant = same as in pre-industrial
Concentration of atmospheric trace gases:
CO2 = 280 ppm
CH4 = 650 ppb
N2O = 270 ppb
CFC = 0
O3 = same as in CMIP5 PI
Topography/bathymetry/coastlines : unchanged compared to pre-industrial
Vegetation and land surface:
Computed using a dynamical vegetation module,
Or prescribed as in PI, with phenology computed for models with active carbon cycle or prescribed from data
No change in ice sheet extent
Interactive, with atmospheric concentration prescribed and ocean and land carbon fluxes diagnosed as recommended in CMIP5
We invite the modelling groups planning to run simulations with an interactive dust cycle to comment on the most appropriate methodology for their model, in particular as to their ability to use a interactive vegetation description.