Paleoclimate Modelling Intercomparison Project
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| Paleoclimate Modelling Intercomparison Project | |
|---|---|
| Name | Paleoclimate Modelling Intercomparison Project |
| Abbr | PMIP |
| Formation | 1990 |
| Type | Scientific collaboration |
| Purpose | Paleoclimate model intercomparison and evaluation |
| Region | Global |
| Parent organization | World Climate Research Programme |
Paleoclimate Modelling Intercomparison Project is an international collaboration that coordinates systematic comparisons of numerical climate model simulations of past climate states. It brings together modeling groups, observational synthesists, and archival centers to evaluate representations of past climate change during intervals such as the Last Glacial Maximum, the Holocene, the Mid-Holocene, and the Pliocene. The project informs model development used by assessments from organizations like the Intergovernmental Panel on Climate Change and guides interpretation of proxy records from institutions such as the National Oceanic and Atmospheric Administration and the British Geological Survey.
Overview and Objectives
The primary objective is to standardize experiments that test general circulation model performance against palaeoclimate evidence, enabling intercomparison across modeling frameworks developed at centers such as Met Office Hadley Centre, National Center for Atmospheric Research, Max Planck Institute for Meteorology, and Geophysical Fluid Dynamics Laboratory. Goals include evaluating paleoclimate sensitivity invoked in Coupled Model Intercomparison Project studies, benchmarking model skill with proxy compilations from initiatives like PAGES and the Neotoma Paleoecology Database, and improving representations of processes described in literature from James Hansen, Wally Broecker, and Sukyoung Lee. PMIP provides standardized boundary conditions and forcings aligned with datasets from Paleoclimate Modelling Intercomparison Project Phase 4 contributors and archival practices used by the Earth System Grid Federation.
History and Development
PMIP originated as a response to community demand in the late 1980s and formally organized in the early 1990s under the auspices of the World Climate Research Programme and the International Geosphere-Biosphere Programme. Key milestones include early comparisons of simulations by groups at Università degli Studi di Milano, University of Bern, and Institut Pierre-Simon Laplace, expansion into multiproxy syntheses coordinated with researchers such as Jacques Labeyrie and Lonnie Thompson, and formal phases labeled PMIP1 through PMIP4 that aligned with successive IPCC Assessment Reports. Workshops hosted by institutions like University of Colorado Boulder, ETH Zurich, and Potsdam Institute for Climate Impact Research set experimental protocols and fostered collaborations with proxy specialists at Lamont–Doherty Earth Observatory and Scripps Institution of Oceanography.
Participating Models and Experiments
Participants include modeling centers that develop atmosphere–ocean general circulation models, Earth system models, and intermediate complexity models from organizations such as CSIRO, CNRM, Météo-France, CNR, and Institute of Atmospheric Physics (China). Standard experiments have encompassed simulations of the Last Glacial Maximum, mid-Holocene, Last Interglacial, and transient runs spanning the deglaciation and the Pleistocene-Holocene transition. PMIP coordinates with other initiatives including Paleoclimate Modelling Intercomparison Project Phase 4 and PMIP3 linkages to CMIP5 and CMIP6 experiments to compare paleoclimate constraints on model equilibrium climate sensitivity used in IPCC Special Report assessments.
Methodologies and Protocols
PMIP issues detailed protocols specifying boundary conditions (ice sheet reconstructions from Peltier (ICE-5G), greenhouse gas concentrations following Ice-core records from Vostok and EPICA), orbital parameters derived from calculations by Milankovitch theory, and land-surface datasets compiled with contributions from US Geological Survey and European Space Agency. Standardization includes spin-up procedures, coupling strategies for ocean general circulation model components, and output conventions compatible with the Climate and Forecast (CF) metadata and the NetCDF data model used by the Earth System Grid Federation. Model–data comparisons utilize proxy calibration datasets and statistical techniques advanced by researchers at University of Washington, University of Cambridge, and ETH Zurich.
Key Findings and Contributions
PMIP has demonstrated robust model responses to major boundary condition changes consistent with palaeoproxy syntheses from Marine Isotope Stage 3 archives, pollen records from the European Pollen Database, and ice-core isotopic reconstructions from Greenland Ice Sheet Project cores. Contributions include refined estimates of climate sensitivity through comparison of Pliocene warming experiments with paleobotanical data from institutions like Smithsonian Institution, improved understanding of regional monsoon dynamics tied to Indian Monsoon reconstructions, and evaluation of feedbacks involving ice sheets and vegetation that inform projections used by IPCC Working Group I. PMIP outputs underpin paleo-reanalyses and data assimilation efforts conducted at centers such as NOAA PSL.
Challenges and Limitations
Challenges include uncertainties in boundary conditions generated by competing reconstructions from groups like ICE-6G and discrepancies among proxy datasets sourced from the Neotoma Paleoecology Database, PAGES 2k and regional syntheses. Limitations arise from model resolution constraints faced by laboratories such as Los Alamos National Laboratory and simplified process representations in intermediate models from University of Victoria. Additional difficulties stem from intercomparison of ensembles with differing aerosol schemes used by IPSL and bias correction methods developed at Met Office Hadley Centre, complicating attribution of model–data mismatches.
Impact on Climate Science and Policy
PMIP has directly influenced assessments by the Intergovernmental Panel on Climate Change and guided climate model development at agencies like NOAA, NASA Goddard Institute for Space Studies, and European Centre for Medium-Range Weather Forecasts. Its standardized experiments and archived outputs support international initiatives in palaeoclimate research organized by PAGES, the World Climate Research Programme, and the International Geosphere-Biosphere Programme, informing policy-relevant synthesis reports produced for bodies such as the United Nations Framework Convention on Climate Change and national science academies including the Royal Society and the National Academy of Sciences. PMIP’s legacy includes strengthened links between proxy scientists and modelers, improved confidence bounds for past climate states, and enhanced use of deep-time analogues in scenario evaluation for policy makers.