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.
Highlights
Global climate projections using climate models were based on simulations using atmosphere-only physical models (Manabe et al, 1965)
When comparing the net top of atmosphere (TOA) radiation balance of the historical simulation (HIST) simulation with satellite measurements (CERES EBAF-TOA edition 4.0 constrained by in situ measurements; Loeb et al, 2012, 2018), the model result is −0.63 W m−2 during 2001–2010, which is within the range of −0.5 ± 0.43 W m−2 estimated by Loeb et al (2012) for the corresponding period (Fig. 2a)
Earth system model (ESM), respectively, and the horizontal bars represent the range of the Coupled Model Intercomparison Project Phase 5 (CMIP5) ESMs
Summary
Global climate projections using climate models were based on simulations using atmosphere-only physical models (Manabe et al, 1965). Cox et al (2000) attempted to couple a carbon cycle model and a climate model to investigate the roles of biophysical and biogeochemical (carbon cycle) feedbacks on climate. Their results showed that such interactions are significant in projecting future climate due to processes and feedbacks beyond those incorporated in traditional climate models. The most comprehensive state-of-the-art ESMs include component models of the land and ocean carbon cycle, atmospheric chemistry, dynamic vegetation, and other biogeochemical cycles (e.g., Watanabe et al, 2011; Collins et al, 2011)
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