Session: Last Millennium & Past2K
Author: Johann Jungclaus / email@example.com / Max Planck Institute for Meteorology, Hamburg, Germany
Co-author: Past2k Working Group, ;
The working group “Past2k” aims at:
• Promoting community simulations of the Late Holocene with state-of-the-art Earth System Models (ESM), such as the PMIP4/CMIP6 “past1000” experiments; coordinating the experimental design and analysis framework
• Coordinating collaborative effort to asses model performance and process-based analysis
• Promoting model-data comparison activities cooperating with climate reconstruction groups, statisticians, and dynamicists
The WG has coordinated and initiated efforts to update the experimental protocol and reconstructions of external forcing, such as solar irradiance and volcanic aerosols as well as a data protocol. The manuscript, published in GMD as part 3 of a series of PMIP papers, discusses in detail the forcing agents: orbital, solar, volcanic, land-use/land-cover changes, and variations in greenhouse gas concentrations. The past1000 simulations covering the pre-industrial millennium from 850 Common Era (CE) to 1849 CE have to be complemented by historical simulations (1850 to 2014 CE) following the CMIP6 protocol. The external forcings for the past1000 experiments have been adapted to provide a seamless transition across these time periods. Protocols for the past1000 simulations have been divided into three tiers. A default forcing data set has been defined for the “tier-1” (the CMIP6 past1000) experiment. However, the PMIP community has maintained the flexibility to conduct coordinated sensitivity experiments to explore uncertainty in forcing reconstructions as well as parameter uncertainty in dedicated “tier-2” simulations. Additional experiments (“tier-3”) are defined to foster collaborative model experiments focusing on the early instrumental period and to extend the temporal range and the scope of the simulations.
On-going efforts regarding model-data comparison have focused on regional temperature reconstructions and have extended the scope of target variables to assess hydroclimatic reconstructions. A workshop was held in Lamont in June 2016 as a joint effort of PAGES 2K and the PMIP PastK working group. The aim oft he meeting was to review CE proxy archives appropriate for hydroclimate assessment and the current ensemble of coupled model simulations. The participants discussed outstanding challenges and made recommendations for best practices for how to perform reconstruction-model intercomparisons for hydroclimate.