Development of the MIROC-ES2L Earth system model and the evaluation of biogeochemical processes and feedbacks

Abstract

Abstract. This article describes the new Earth system model (ESM), the Model for Interdisciplinary Research on Climate, Earth System version 2 for Long-term simulations (MIROC-ES2L), using a state-of-the-art climate model as the physical core. This model embeds a terrestrial biogeochemical component with explicit carbon–nitrogen interaction to account for soil nutrient control on plant growth and the land carbon sink. The model's ocean biogeochemical component is largely updated to simulate the biogeochemical cycles of carbon, nitrogen, phosphorus, iron, and oxygen such that oceanic primary productivity can be controlled by multiple nutrient limitations. The ocean nitrogen cycle is coupled with the land component via river discharge processes, and external inputs of iron from pyrogenic and lithogenic sources are considered. Comparison of a historical simulation with observation studies showed that the model could reproduce the transient global climate change and carbon cycle as well as the observed large-scale spatial patterns of the land carbon cycle and upper-ocean biogeochemistry. The model demonstrated historical human perturbation of the nitrogen cycle through land use and agriculture and simulated the resultant impact on the terrestrial carbon cycle. Sensitivity analyses under preindustrial conditions revealed that the simulated ocean biogeochemistry could be altered regionally (and substantially) by nutrient input from the atmosphere and rivers. Based on an idealized experiment in which CO2 was prescribed to increase at a rate of 1 % yr−1, the transient climate response (TCR) is estimated to be 1.5 K, i.e., approximately 70 % of that from our previous ESM used in the Coupled Model Intercomparison Project Phase 5 (CMIP5). The cumulative airborne fraction (AF) is also reduced by 15 % because of the intensified land carbon sink, which results in an airborne fraction close to the multimodel mean of the CMIP5 ESMs. The transient climate response to cumulative carbon emissions (TCRE) is 1.3 K EgC−1, i.e., slightly smaller than the average of the CMIP5 ESMs, which suggests that “optimistic” future climate projections will be made by the model. This model and the simulation results contribute to CMIP6. The MIROC-ES2L could further improve our understanding of climate–biogeochemical interaction mechanisms, projections of future environmental changes, and exploration of our future options regarding sustainable development by evolving the processes of climate, biogeochemistry, and human activities in a holistic and interactive manner.

Carbon–concentration and carbon–climate feedbacks in CMIP6 models and their comparison to CMIP5 models

“…The reason for this is that the positive feedbacks associated with various aspects of the climate system enhance the initial warming. These primarily include changes in atmospheric water vapour, tropospheric lapse rate, surface albedo resulting from ice and snow, and clouds (Hansen et al, 1984;Gregory et al, 2009;Ceppi and Gregory, 2017).…”

A Bayesian framework for emergent constraints: case studies of climate sensitivity with PMIP

“…Consequently, an observation of one measurable variable (such as past tropical temperatures) could be used to better constrain the other investigated variable, usually unobserved and difficult to measure (such as climate sensitivity). This idea has been used in climate science to estimate quantities of interest such as snow albedo feedback (Hall and Qu, 2006), future sea ice extent (Boé et al, 2009;Notz, 2015), low-level cloud feedback (Brient et al, 2016), and the equilibrium climate sensitivity (Hargreaves et al, 2012;Schmidt et al, 2014;Cox et al, 2018). Although the unobserved variable is usually taken as a future variable, the emergent constraints theory can be used with two variables within the same timeframe, as long as the relationship is plausible.…”

“…In recent years, researchers have identified a number of relationships between observational properties and a future climate change, which was not immediately obvious a priori but which exists across the ensemble of global climate models (GCMs) (Allen and Ingram, 2002;Hall and Qu, 2006;Boé et al, 2009;Cox et al, 2018) participating in the Climate Model Intercomparison Project (CMIP). These relationships are generally referred to as "emergent constraints" as they emerge from the ensemble behaviour as a whole rather than from explicit physical analysis.…”

Biogeophysical and biogeochemical impacts of land-use change simulated by MIROC-ES2L

“…MIROC is a global climate model developed mainly by the University of Tokyo and the Japan Agency for Marine-Earth Science and Technology. Hajima et al (2020) developed MIROC-ES2L by incorporating biogeochemical processes into the well-tested MIROC general circulation model for atmospheric and oceanic physical processes (Tatebe et al 2019). The horizontal resolution of the atmospheric component of MIROC-ES2L is approximately 2.8°for latitude and longitude (T42 spectral truncation), and the vertical resolution is 40 layers up to 3 hPa.…”

“…As a part of the LUMIP, a series of experiments was proposed to evaluate the biophysical and biogeochemical impacts of land-use change associated with different drivers. This study investigated land-use impacts simulated by the Model for Interdisciplinary Research on Climate, Earth System version 2 for Long-term simulations (MIROC-ES2L) (Hajima et al 2020), which has been used for climate projections expected to contribute to the next assessment report of the Intergovernmental Panel on Climate Change. We first briefly describe the land-use scheme in the MIROC-ES2L, and then, we present preliminary results of simulations of land-use impacts conducted under the LUMIP protocol.…”