Abstract
Abstract. The mid-Holocene (6000 years ago) is a standard time period for the evaluation of the simulated response of global climate models using palaeoclimate reconstructions. The latest mid-Holocene simulations are a palaeoclimate entry card for the Palaeoclimate Model Intercomparison Project (PMIP4) component of the current phase of the Coupled Model Intercomparison Project (CMIP6) – hereafter referred to as PMIP4-CMIP6. Here we provide an initial analysis and evaluation of the results of the experiment for the mid-Holocene. We show that state-of-the-art models produce climate changes that are broadly consistent with theory and observations, including increased summer warming of the Northern Hemisphere and associated shifts in tropical rainfall. Many features of the PMIP4-CMIP6 simulations were present in the previous generation (PMIP3-CMIP5) of simulations. The PMIP4-CMIP6 ensemble for the mid-Holocene has a global mean temperature change of −0.3 K, which is −0.2 K cooler than the PMIP3-CMIP5 simulations predominantly as a result of the prescription of realistic greenhouse gas concentrations in PMIP4-CMIP6. Biases in the magnitude and the sign of regional responses identified in PMIP3-CMIP5, such as the amplification of the northern African monsoon, precipitation changes over Europe, and simulated aridity in mid-Eurasia, are still present in the PMIP4-CMIP6 simulations. Despite these issues, PMIP4-CMIP6 and the mid-Holocene provide an opportunity both for quantitative evaluation and derivation of emergent constraints on the hydrological cycle, feedback strength, and potentially climate sensitivity.
Highlights
Future climate changes pose a major challenge for Human civilisation, yet uncertainty remains about the nature of those changes
Combining regional benchmarking of model performance with process diagnosis – to ensure that a model is correct because it captures the right processes – would provide a firmer basis for using the midHolocene simulations to enhance our confidence in future projections
The PMIP4-CMIP6 midHolocene simulations show changes in seasonal temperatures and precipitation that are in line with the theoretical response to changes in insolation forcing
Summary
Future climate changes pose a major challenge for Human civilisation, yet uncertainty remains about the nature of those changes. The Coupled Model Intercomparison Project (CMIP; Eyring et al, 2016), which coordinates efforts to compare climate model simulations, includes simulations designed to test model performance under past climate regimes. Evaluation of these palaeoclimate simulations against palaeoclimate reconstructions, coordinated through the Palaeoclimate Modelling Intercomparison Project (PMIP; Kageyama et al, 2018), provides an independent test of the ability of state-of-the-art models to simulate climate change
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