scholarly journals Role of AMOC in Transient Climate Response to Greenhouse Gas Forcing in Two Coupled Models

2020 ◽  
Vol 33 (14) ◽  
pp. 5845-5859
Author(s):  
Aixue Hu ◽  
Luke Van Roekel ◽  
Wilbert Weijer ◽  
Oluwayemi A. Garuba ◽  
Wei Cheng ◽  
...  
Keyword(s):  
Greenhouse Gas ◽  
Climate Sensitivity ◽  
Earth System Model ◽  
System Model ◽  
Upper Ocean ◽  
Climate Response ◽  
Earth System ◽  
Transient Climate Response ◽  
Model Version ◽  
The Mean

AbstractAs the greenhouse gas concentrations increase, a warmer climate is expected. However, numerous internal climate processes can modulate the primary radiative warming response of the climate system to rising greenhouse gas forcing. Here the particular internal climate process that we focus on is the Atlantic meridional overturning circulation (AMOC), an important global-scale feature of ocean circulation that serves to transport heat and other scalars, and we address the question of how the mean strength of AMOC can modulate the transient climate response. While the Community Earth System Model version 2 (CESM2) and the Energy Exascale Earth System Model version 1 (E3SM1) have very similar equilibrium/effective climate sensitivity, our analysis suggests that a weaker AMOC contributes in part to the higher transient climate response to a rising greenhouse gas forcing seen in E3SM1 by permitting a faster warming of the upper ocean and a concomitant slower warming of the subsurface ocean. Likewise the stronger AMOC in CESM2 by permitting a slower warming of the upper ocean leads in part to a smaller transient climate response. Thus, while the mean strength of AMOC does not affect the equilibrium/effective climate sensitivity, it is likely to play an important role in determining the transient climate response on the centennial time scale.

scholarly journals High Climate Sensitivity in the Community Earth System Model Version 2 (CESM2)

2019 ◽  
Vol 46 (14) ◽  
pp. 8329-8337 ◽  
Author(s):  
A. Gettelman ◽  
C. Hannay ◽  
J. T. Bacmeister ◽  
R. B. Neale ◽  
A. G. Pendergrass ◽  
...  
Keyword(s):  
Climate Sensitivity ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Model Version ◽  
Community Earth System Model

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

2020 ◽  
Vol 13 (5) ◽  
pp. 2197-2244 ◽  
Author(s):  
Tomohiro Hajima ◽  
Michio Watanabe ◽  
Akitomo Yamamoto ◽  
Hiroaki Tatebe ◽  
Maki A. Noguchi ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Nitrogen Cycle ◽  
Carbon Sink ◽  
Earth System Model ◽  
System Model ◽  
Climate Projections ◽  
Climate Response ◽  
Earth System ◽  
Transient Climate Response ◽  
Ocean Biogeochemistry

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.

Modelling choices with regard to aerosol-cloud interactions and their impact on effective climate sensitivity in the NorESM2 model

2021 ◽  
Author(s):  
Sabine Undorf ◽  
Frida Bender
Keyword(s):  
Climate Change ◽  
Climate Sensitivity ◽  
Liquid Water ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Anthropogenic Aerosols ◽  
Aerosol Cloud ◽  
Model Version ◽  
Aerosol Cloud Interactions

<p>Aerosol-cloud interactions (ACIs) continue to be subject to much uncertainty, supporting a large set of parametric and structural variants of a global climate or Earth System Model (ESM), especially regarding its aerosol and cloud microphysics components. This structural model uncertainty is relevant not only for the quantification of the climate response to anthropogenic aerosols: Because aerosol-cloud interactions are at the core of cloud and precipitation formation, they might also affect model-simulated cloud adjustments and feedbacks in response to greenhouse gases, and hence the model’s effective climate sensitivity (ECS). In-situ observations, satellite retrievals, and large-eddy simulations point to discrepancies between the effects of aerosol-cloud interactions in the real world and as modelled in ESMs, with potential implications for the model range also for ECS. </p><p>Here, we explore how different choices in ACI modelling affect the model’s ECS. For this case study the CMIP6-generation Norwegian Earth System Model version 2 (NorESM2) is used, which has a sophisticated aerosol module and in its ‘default’ version contributed to the CMIP6 suite relatively weak positive cloud feedbacks compared to the other models within the 150 years used to calculate the regression-based ECS (EffCS). The climate change feedback and hence ECS of each modified model version compared to that of the default one is estimated by prescribing a uniform rise of 4K in the sea-surface temperature boundary conditions and evaluating the resulting top-of-atmosphere imbalance difference. A similar or better representation of present-day mean climate in general and ACI effects in particular is ensured by comparing a suite of evaluation metrics with their observationally derived pendants and results from the literature.</p><p>The ACI effects and relevant model-observation discrepancies targeted with the model modifications include models’ excessive cloud brightening over stratocumulus regions compared to satellite products, excessive increase in liquid water path associated with increased aerosol amount, and model bias in the climatological fraction between supercooled liquid water and cloud ice in mixed-phase clouds. For each of these, experiments with multiple combinations of modifications in the model code are analysed, exemplifying the numerous different processes and parameters that together determine the model response. The findings complement approaches to explore models’ parameter spaces systematically by informing the choices physically and restricting the modifications not only to parametric changes. The range of models obtained sets the default NorESM2 version, with its ECS being part of the CMIP6 ensemble, into the context of ACI uncertainty, informs on the so far possibly underappreciated relevance of ACIs for climate change beyond anthropogenic aerosols, and suggests alternative parameterisations for future ‘default’ model versions.</p><div>2.11.0.0</div>

scholarly journals The Norwegian Earth System Model, NorESM1-M – Part 2: Climate response and scenario projections

2013 ◽  
Vol 6 (2) ◽  
pp. 389-415 ◽  
Author(s):  
T. Iversen ◽  
M. Bentsen ◽  
I. Bethke ◽  
J. B. Debernard ◽  
A. Kirkevåg ◽  
...  
Keyword(s):  
Global Climate Model ◽  
Earth System Model ◽  
System Model ◽  
Climate Response ◽  
Earth System ◽  
Atlantic Sector ◽  
Transient Climate Response ◽  
Near Surface ◽  
Enso Events ◽  
Model Average

Abstract. NorESM is a generic name of the Norwegian earth system model. The first version is named NorESM1, and has been applied with medium spatial resolution to provide results for CMIP5 (http://cmip-pcmdi.llnl.gov/cmip5/index.html) without (NorESM1-M) and with (NorESM1-ME) interactive carbon-cycling. Together with the accompanying paper by Bentsen et al. (2012), this paper documents that the core version NorESM1-M is a valuable global climate model for research and for providing complementary results to the evaluation of possible anthropogenic climate change. NorESM1-M is based on the model CCSM4 operated at NCAR, but the ocean model is replaced by a modified version of MICOM and the atmospheric model is extended with online calculations of aerosols, their direct effect and their indirect effect on warm clouds. Model validation is presented in the companion paper (Bentsen et al., 2012). NorESM1-M is estimated to have equilibrium climate sensitivity of ca. 2.9 K and a transient climate response of ca. 1.4 K. This sensitivity is in the lower range amongst the models contributing to CMIP5. Cloud feedbacks dampen the response, and a strong AMOC reduces the heat fraction available for increasing near-surface temperatures, for evaporation and for melting ice. The future projections based on RCP scenarios yield a global surface air temperature increase of almost one standard deviation lower than a 15-model average. Summer sea-ice is projected to decrease considerably by 2100 and disappear completely for RCP8.5. The AMOC is projected to decrease by 12%, 15–17%, and 32% for the RCP2.6, 4.5, 6.0, and 8.5, respectively. Precipitation is projected to increase in the tropics, decrease in the subtropics and in southern parts of the northern extra-tropics during summer, and otherwise increase in most of the extra-tropics. Changes in the atmospheric water cycle indicate that precipitation events over continents will become more intense and dry spells more frequent. Extra-tropical storminess in the Northern Hemisphere is projected to shift northwards. There are indications of more frequent occurrence of spring and summer blocking in the Euro-Atlantic sector, while the amplitude of ENSO events weakens although they tend to appear more frequently. These indications are uncertain because of biases in the model's representation of present-day conditions. Positive phase PNA and negative phase NAO both appear less frequently under the RCP8.5 scenario, but also this result is considered uncertain. Single-forcing experiments indicate that aerosols and greenhouse gases produce similar geographical patterns of response for near-surface temperature and precipitation. These patterns tend to have opposite signs, although with important exceptions for precipitation at low latitudes. The asymmetric aerosol effects between the two hemispheres lead to a southward displacement of ITCZ. Both forcing agents, thus, tend to reduce Northern Hemispheric subtropical precipitation.

scholarly journals Marine biogeochemical cycling and oceanic CO<sub>2</sub> uptake simulated by the NUIST Earth System Model version 3 (NESM v3)

2020 ◽  
Vol 13 (7) ◽  
pp. 3119-3144
Author(s):  
Yifei Dai ◽  
Long Cao ◽  
Bin Wang
Keyword(s):  
Primary Production ◽  
Carbon Concentration ◽  
Large Scale ◽  
Net Primary Production ◽  
Earth System Model ◽  
System Model ◽  
Upper Ocean ◽  
Co2 Uptake ◽  
Earth System ◽  
Model Version

Abstract. In this study, we evaluate the performance of the Nanjing University of Information Science and Technology (NUIST) Earth System Model version 3 (hereafter NESM v3) in simulating the marine biogeochemical cycle and carbon dioxide (CO2) uptake. Compared with observations, the NESM v3 reproduces the large-scale patterns of biogeochemical fields reasonably well in the upper ocean, including nutrients, alkalinity, dissolved inorganic, chlorophyll, and net primary production. Some discrepancies between model simulations and observations are identified and the possible causes are investigated. In the upper ocean, the simulated biases in biogeochemical fields are mainly associated with shortcomings in the simulated ocean circulation. Weak upwelling in the Indian Ocean suppresses the nutrient entrainment to the upper ocean, thus reducing biological activities and resulting in an underestimation of net primary production and the chlorophyll concentration. In the Pacific and the Southern Ocean, nutrients are overestimated as a result of strong iron limitation and excessive vertical mixing. Alkalinity is also overestimated in high-latitude oceans due to excessive convective mixing. The major discrepancy in biogeochemical fields is that the model overestimates nutrients, alkalinity, and dissolved inorganic carbon in the deep North Pacific, which is caused by the excessive deep ocean remineralization. The model reasonably reproduces present-day oceanic CO2 uptake. Model-simulated cumulative oceanic CO2 uptake is 149 PgC between 1850 and 2016, which compares well with data-based estimates of 150±20 PgC. In the 1 % yr−1 CO2 increase (1ptCO2) experiment, the diagnosed carbon-climate (γ=-7.9 PgC K−1) and carbon-concentration sensitivity parameters (β=0.88 PgC ppm−1) in the NESM v3 are comparable with those in Coupled Model Intercomparison Project phase 5 (CMIP5) models (β: 0.69 to 0.91 PgC ppm−1; γ: −2.4 to −12.1 PgC K−1). The nonlinear interaction between carbon-concentration and carbon-climate sensitivity in the NESM v3 accounts for 10.3 % of the total carbon uptake, which is within the range of CMIP5 model results (3.6 %–10.6 %). Overall, the NESM v3 can be employed as a useful modeling tool to investigate large-scale interactions between the ocean carbon cycle and climate change.

CO2 increase experiments using the Community Earth System Model (CESM): Relationship to climate sensitivity and comparison of CESM1 to CESM2

2020 ◽  
Author(s):  
Julio T. Bacmeister ◽  
Cecile Hannay ◽  
Brian Medeiros ◽  
Andrew Gettelman ◽  
Richard Neale ◽  
...  
Keyword(s):  
Climate Sensitivity ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Community Earth System Model

The Madden-Julian Oscillation in the Energy Exascale Earth System Model Version 1

2021 ◽  
Author(s):  
Daehyun Kim ◽  
Daehyun Kang ◽  
Min-Seop Ahn ◽  
Charlotte DeMott ◽  
Chia-Wei Hsu ◽  
...  
Keyword(s):  
Earth System Model ◽  
System Model ◽  
Madden Julian Oscillation ◽  
Earth System ◽  
Model Version
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