Large-scale features and evaluation of the PMIP4-CMIP6 <i>midHolocene</i> simulations

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.

PMIP4 experiments using MIROC-ES2L Earth system model

“…S4). The simulated glacial ocean is therefore unable to explain the glacial-interglacial drawdown of atmospheric CO 2 , which is similar to previous modeling studies (Buchanan et al, 2016). It should be noted that the effects of burial-nutrient feedback and carbonate compensation on the oceanic carbon cycle are not considered in this simulation because MIROC-ES2L does not include a sediment module.…”

Large-scale features of Last Interglacial climate: results from evaluating the <i>lig127k</i> simulations for the Coupled Model Intercomparison Project (CMIP6)–Paleoclimate Modeling Intercomparison Project (PMIP4)

“…No robust relationship to the August-September lig127k minimum Arctic sea ice area anomaly is present. This is also true for the CMIP6-PMIP4 mid Holocene simulations (Brierley et al, 2020). One reason for a lack of any relationship may be the seasonal nature of the lig127k and midHolocene insolation forcings as compared to the annual forcing by greenhouse gas changes in future projections.…”

“…Not considering the "paleo-calendar effect" can prevent the correct interpretation of data and model comparisons at 127 ka, with the largest problems occurring in boreal fall/austral spring (Joussaume and Braconnot, 1997;Bartlein and Shafer, 2019). A more detailed discussion of the application of the PaleoCal-Adjust software to past time periods with strong orbital forcing can be found in Bartlein and Shafer (2019) and Brierley et al (2020). Brierley et al (2020) provide an extensive evaluation of the CMIP6 preindustrial simulations as compared to observational datasets: reanalyzed climatological temperatures (between 1871-1900 CE; Compo et al, 2011) for the spatial patterns, zonal averages of observed temperature for the period 1850-1900 CE from the HadCRUT4 dataset (Morice et al, 2012;Ilyas et al, 2017), and climatological precipitation data for the period between 1970 and the present day (Adler et al, 2003).…”

“…A more detailed discussion of the application of the PaleoCal-Adjust software to past time periods with strong orbital forcing can be found in Bartlein and Shafer (2019) and Brierley et al (2020). Brierley et al (2020) provide an extensive evaluation of the CMIP6 preindustrial simulations as compared to observational datasets: reanalyzed climatological temperatures (between 1871-1900 CE; Compo et al, 2011) for the spatial patterns, zonal averages of observed temperature for the period 1850-1900 CE from the HadCRUT4 dataset (Morice et al, 2012;Ilyas et al, 2017), and climatological precipitation data for the period between 1970 and the present day (Adler et al, 2003). In summary, they find that the PMIP4-CMIP6 models are in general cooler than the observations, most noticeably at the poles, over land, and over the NH oceans.…”

African Humid Period Precipitation Sustained by Robust Vegetation, Soil, and Lake Feedbacks

“…The recognition that in the past the Sahara had existed in states very different from that of today has always generated interest in the climate dynamics of the region and served as the primary motive for studying the AHP. One interval during the AHP that has received a great amount of interest from both modeling (Braconnot et al, 2012; The mid-Holocene has emerged as a reference case for interrogating the dynamics of the AHP and its primary atmospheric feature-the West African Monsoon (WAM), in part because of its inclusion as a baseline experiment in the Paleoclimate Modelling Intercomparison Project (PMIP) since its inception in the early 1990s (Joussaume & Taylor, 1995Otto-Bliesner et al, 2017). Results from modeling studies performed over the past few decades have revealed the crucial role that feedback processes, such as feedbacks from the ocean (Kutzbach & Liu, 1997), land surface (Broström et al, 1998;Ganopolski et al, 1998;Krinner et al, 2012;Levis et al, 2004) and dust (Egerer et al, 2016;Pausata et al, 2016), play in enhancing the WAM so that it could support the AHP (Claussen et al, 2017).…”