Can an Earth System Model simulate better climate change at mid-Holocene than an AOGCM? A comparison study of MIROC-ESM and MIROC3

Abstract

The importance of evaluating models through paleoclimate simulations is becoming more recognized in efforts to improve climate projection. To evaluate an integrated Earth System Model, MIROC-ESM, we performed simulations in time-slice experiments for the mid-Holocene (6000 yr before present, 6 ka) and preindustrial (1850 AD, 0 ka) periods under the protocol of the Coupled Model Intercomparison Project 5/Paleoclimate Modelling Intercomparison Project 3. We first give an overview of the simulated global climates by comparing with simulations using a previous version of the MIROC model (MIROC3), which is an atmosphere–ocean coupled general circulation model. We then comprehensively discuss various aspects of climate change with 6 ka forcing and how the differences in the models can affect the results. We also discuss the representation of the precipitation enhancement at 6 ka over northern Africa. The precipitation enhancement at 6 ka over northern Africa according to MIROC-ESM does not differ greatly from that obtained with MIROC3, which means that newly developed components such as dynamic vegetation and improvements in the atmospheric processes do not have significant impacts on the representation of the 6 ka monsoon change suggested by proxy records. Although there is no drastic difference between the African monsoon representations of the two models, there are small but significant differences in the precipitation enhancement over the Sahara in early summer, which can be related to the representation of the sea surface temperature rather than the vegetation coupling in MIROC-ESM. Because the oceanic parts of the two models are identical, the difference in the sea surface temperature change is ultimately attributed to the difference in the atmospheric and/or land modules, and possibly the difference in the representation of low-level clouds

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

“…7). This is a region where previous analyses have shown that simulated changes in monsoon rainfall reflect the competition between enhanced contrast in moist static energy between land and ocean and increased local evaporation over the warmer oceans (Ohgaito et al, 2013). Ensemble mean changes in the North American Monsoon System, and the Southern Hemisphere monsoons are also small ( Fig.…”

What have we learnt from palaeoclimate simulations?

“…The explicit simulation of these components of the climate system greatly facilitates comparisons with natural records (e.g. Wasson and Claussen, ; Ohgaito et al ., ).…”

Description of the MIROC-ES2L Earth system model and evaluation of its climate–biogeochemical processes and feedbacks

“…In particular, nutrients in 110 the upper ocean are sustained by upwelling from the deeper ocean and nutrient inputs from external sources. Some studies suggest that nutrient availability to marine ecosystems could decline in the future through reduction of nutrient upwelling because of intensified stratification (e.g., Ono et al, 2008;Whitney et al, 2013;Yasunaka et al, 2016). Conversely, other https://doi.org/10.5194/gmd-2019-275 Preprint.…”

“…For land, the Minimal Advanced Treatments of 195 Surface Interaction and Runoff (MATSIRO) model (Takata et al, 2003) is coupled to simulate the atmosphere-land boundary conditions and freshwater input into the ocean. Considering the application possibility of the ESM to long-term climate simulations of more than hundreds of years, e.g., paleoclimate studies (Ohgaito et al, 2013;Yamamoto et al, 2019), the horizontal resolution of the atmosphere is set to have T42 spectral truncation, which is approximately 2.8° intervals for latitude and longitude. The vertical resolution is 40 layers up to 3 hPa with a hybrid σ-p coordinate, as in 200 MIROC5.…”