Abstract
Abstract. This paper is the first of a series of four GMD papers on the PMIP4-CMIP6 experiments. Part 2 (Otto-Bliesner et al., 2017) gives details about the two PMIP4-CMIP6 interglacial experiments, Part 3 (Jungclaus et al., 2017) about the last millennium experiment, and Part 4 (Kageyama et al., 2017) about the Last Glacial Maximum experiment. The mid-Pliocene Warm Period experiment is part of the Pliocene Model Intercomparison Project (PlioMIP) – Phase 2, detailed in Haywood et al. (2016).The goal of the Paleoclimate Modelling Intercomparison Project (PMIP) is to understand the response of the climate system to different climate forcings for documented climatic states very different from the present and historical climates. Through comparison with observations of the environmental impact of these climate changes, or with climate reconstructions based on physical, chemical, or biological records, PMIP also addresses the issue of how well state-of-the-art numerical models simulate climate change. Climate models are usually developed using the present and historical climates as references, but climate projections show that future climates will lie well outside these conditions. Palaeoclimates very different from these reference states therefore provide stringent tests for state-of-the-art models and a way to assess whether their sensitivity to forcings is compatible with palaeoclimatic evidence. Simulations of five different periods have been designed to address the objectives of the sixth phase of the Coupled Model Intercomparison Project (CMIP6): the millennium prior to the industrial epoch (CMIP6 name: past1000); the mid-Holocene, 6000 years ago (midHolocene); the Last Glacial Maximum, 21 000 years ago (lgm); the Last Interglacial, 127 000 years ago (lig127k); and the mid-Pliocene Warm Period, 3.2 million years ago (midPliocene-eoi400). These climatic periods are well documented by palaeoclimatic and palaeoenvironmental records, with climate and environmental changes relevant for the study and projection of future climate changes. This paper describes the motivation for the choice of these periods and the design of the numerical experiments and database requests, with a focus on their novel features compared to the experiments performed in previous phases of PMIP and CMIP. It also outlines the analysis plan that takes advantage of the comparisons of the results across periods and across CMIP6 in collaboration with other MIPs.
Highlights
Instrumental meteorological and oceanographic data show that the Earth has undergone a global warming of ∼ 0.85 ◦C since the beginning of the Industrial Revolution (Hartmann et al, 2013), largely in response to the increase in atmospheric greenhouse gases
Evaluation of the PMIP3-CMIP5 MH and LGM experiments has demonstrated that climate models simulate changes in the large-scale features that are governed by the energy and water balance reasonably well (Harrison et al, 2014, 2015; Li et al, 2013), including changes in land– sea contrast and high-latitude amplification of temperature changes (Izumi et al, 2013, 2015)
Systematic benchmarking of the PMIP3-CMIP5 MH and LGM shows that better performance in palaeoclimate simulations is not consistently related to better performance under modern conditions, stressing that the ability to simulate modern climate regimes and processes does not guarantee that a model will be good at simulating climate changes (Harrison et al, 2015)
Summary
Instrumental meteorological and oceanographic data show that the Earth has undergone a global warming of ∼ 0.85 ◦C since the beginning of the Industrial Revolution (Hartmann et al, 2013), largely in response to the increase in atmospheric greenhouse gases. (land area is expanded relative to present due to the lower sea level, Fig. 2), and lower atmospheric greenhouse gas concentrations It is a relevant time period for understanding near-future climate change because the magnitude of the forcing and temperature response from the LGM to present is comparable to that projected from present to the end of the 21st century (Braconnot et al, 2012). The major changes in the experimental protocol for lig127k, compared to the pre-industrial DECK experiment, are changes in the astronomical parameters and greenhouse gas concentrations (Table 2 and Otto-Bliesner et al, 2017) Meaningful analyses of these simulations are possible because of the concerted effort to synchronize the chronologies of individual records and provide a spatial–temporal picture of Last Interglacial temperature change (Capron et al, 2014, 2017), and to document the timing of the Greenland and Antarctic contributions to sea level (Winsor et al, 2012; Steig et al, 2015). Boundary conditions (Table 2) include modifications to global ice distributions (Fig. 2), topography/bathymetry, vegetation, and CO2 and are provided by the US Geological Survey Pliocene Research and Synoptic Mapping Project (PRISM4: Dowsett et al, 2016)
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