scholarly journals Equilibrium Climate Sensitivity: Is It Accurate to Use a Slab Ocean Model?

2009 ◽  
Vol 22 (9) ◽  
pp. 2494-2499 ◽  
Author(s):  
Gokhan Danabasoglu ◽  
Peter R. Gent
Keyword(s):  
Carbon Dioxide ◽  
Climate Sensitivity ◽  
Climate Model ◽  
Temperature Response ◽  
Accurate Estimate ◽  
Ocean Model ◽  
Climate System Model ◽  
Equilibrium Climate Sensitivity ◽  
Model Version ◽  
Slab Ocean

Abstract The equilibrium climate sensitivity of a climate model is usually defined as the globally averaged equilibrium surface temperature response to a doubling of carbon dioxide. This is virtually always estimated in a version with a slab model for the upper ocean. The question is whether this estimate is accurate for the full climate model version, which includes a full-depth ocean component. This question has been answered for the low-resolution version of the Community Climate System Model, version 3 (CCSM3). The answer is that the equilibrium climate sensitivity using the full-depth ocean model is 0.14°C higher than that using the slab ocean model, which is a small increase. In addition, these sensitivity estimates have a standard deviation of nearly 0.1°C because of interannual variability. These results indicate that the standard practice of using a slab ocean model does give a good estimate of the equilibrium climate sensitivity of the full CCSM3. Another question addressed is whether the effective climate sensitivity is an accurate estimate of the equilibrium climate sensitivity. Again the answer is yes, provided that at least 150 yr of data from the doubled carbon dioxide run are used.

scholarly journals Climate Sensitivity of the Community Climate System Model, Version 4

2012 ◽  
Vol 25 (9) ◽  
pp. 3053-3070 ◽  
Author(s):  
C. M. Bitz ◽  
K. M. Shell ◽  
P. R. Gent ◽  
D. A. Bailey ◽  
G. Danabasoglu ◽  
...  
Keyword(s):  
Sea Ice ◽  
Climate Sensitivity ◽  
Ocean Model ◽  
System Model ◽  
Climate Response ◽  
Climate System Model ◽  
Equilibrium Climate Sensitivity ◽  
Model Version ◽  
Slab Ocean ◽  
Global Mean

Equilibrium climate sensitivity of the Community Climate System Model, version 4 (CCSM4) is 3.20°C for 1° horizontal resolution in each component. This is about a half degree Celsius higher than in the previous version (CCSM3). The transient climate sensitivity of CCSM4 at 1° resolution is 1.72°C, which is about 0.2°C higher than in CCSM3. These higher climate sensitivities in CCSM4 cannot be explained by the change to a preindustrial baseline climate. This study uses the radiative kernel technique to show that, from CCSM3 to CCSM4, the global mean lapse-rate feedback declines in magnitude and the shortwave cloud feedback increases. These two warming effects are partially canceled by cooling because of slight decreases in the global mean water vapor feedback and longwave cloud feedback from CCSM3 to CCSM4. A new formulation of the mixed layer, slab-ocean model in CCSM4 attempts to reproduce the SST and sea ice climatology from an integration with a full-depth ocean, and it is integrated with a dynamic sea ice model. These new features allow an isolation of the influence of ocean dynamical changes on the climate response when comparing integrations with the slab ocean and full-depth ocean. The transient climate response of the full-depth ocean version is 0.54 of the equilibrium climate sensitivity when estimated with the new slab-ocean model version for both CCSM3 and CCSM4. The authors argue the ratio is the same in both versions because they have about the same zonal mean pattern of change in ocean surface heat flux, which broadly resembles the zonal mean pattern of net feedback strength.

scholarly journals Could the Pliocene constrain the Equilibrium Climate Sensitivity?

2016 ◽  
Author(s):  
J. C. Hargreaves ◽  
J. D. Annan
Keyword(s):  
Carbon Dioxide ◽  
Boundary Conditions ◽  
Climate Sensitivity ◽  
Atmospheric Carbon Dioxide ◽  
Climate Models ◽  
Climate Model ◽  
Equilibrium Climate Sensitivity ◽  
Model Experiments ◽  
First Time ◽  
Industrial State

Abstract. The mid-PlioceneWarm Period (mPWP) is the most recent interval in which atmospheric carbon dioxide was substantially higher than in modern pre-industrial times. It is, therefore, a potentially valuable target for testing the ability of climate models to simulate climates warmer than the pre-industrial state. The recent Pliocene model inter-comparison Project (PlioMIP) presented boundary conditions for the mPWP, and a protocol for climate model experiments. Here we analyse results from the PlioMIP and, for the first time, discuss the potential for this interval to usefully constrain the equilibrium climate sensitivity. We present an estimate of 1.8–3.6 °C, but there are considerable uncertainties surrounding the analysis. We consider the extent to which these uncertainties may be lessened in the next few years.

scholarly journals The HAMMONIA Chemistry Climate Model: Sensitivity of the Mesopause Region to the 11-Year Solar Cycle and CO2 Doubling

2006 ◽  
Vol 19 (16) ◽  
pp. 3903-3931 ◽  
Author(s):  
H. Schmidt ◽  
G. P. Brasseur ◽  
M. Charron ◽  
E. Manzini ◽  
M. A. Giorgetta ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Solar Cycle ◽  
General Circulation ◽  
Climate Model ◽  
Temperature Response ◽  
Circulation Model ◽  
Max Planck ◽  
Dynamical Processes ◽  
Mesopause Region ◽  
Height Range

Abstract This paper introduces the three-dimensional Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), which treats atmospheric dynamics, radiation, and chemistry interactively for the height range from the earth’s surface to the thermosphere (approximately 250 km). It is based on the latest version of the ECHAM atmospheric general circulation model of the Max Planck Institute for Meteorology in Hamburg, Germany, which is extended to include important radiative and dynamical processes of the upper atmosphere and is coupled to a chemistry module containing 48 compounds. The model is applied to study the effects of natural and anthropogenic climate forcing on the atmosphere, represented, on the one hand, by the 11-yr solar cycle and, on the other hand, by a doubling of the present-day concentration of carbon dioxide. The numerical experiments are analyzed with the focus on the effects on temperature and chemical composition in the mesopause region. Results include a temperature response to the solar cycle by 2 to 10 K in the mesopause region with the largest values occurring slightly above the summer mesopause. Ozone in the secondary maximum increases by up to 20% for solar maximum conditions. Changes in winds are in general small. In the case of a doubling of carbon dioxide the simulation indicates a cooling of the atmosphere everywhere above the tropopause but by the smallest values around the mesopause. It is shown that the temperature response up to the mesopause is strongly influenced by changes in dynamics. During Northern Hemisphere summer, dynamical processes alone would lead to an almost global warming of up to 3 K in the uppermost mesosphere.

Why does the climate response to greenhouse warming and greenhouse cooling differ? 

2021 ◽  
Author(s):  
Jennifer Kay ◽  
Jason Chalmers
Keyword(s):  
Carbon Dioxide ◽  
Radiative Forcing ◽  
Climate Model ◽  
Temperature Response ◽  
Greenhouse Warming ◽  
Climate Response ◽  
Cloud Feedbacks ◽  
Surface Climate ◽  
Carbon Dioxide Concentrations ◽  
Radiative Feedbacks

<p>While the long-standing quest to constrain equilibrium climate sensitivity has resulted in intense scrutiny of the processes controlling idealized greenhouse warming, the processes controlling idealized greenhouse cooling have received less attention. Here, differences in the climate response to increased and decreased carbon dioxide concentrations are assessed in state-of-the-art fully coupled climate model experiments. One hundred and fifty years after an imposed instantaneous forcing change, surface global warming from a carbon dioxide doubling (abrupt-2xCO2, 2.43 K) is larger than the surface global cooling from a carbon dioxide halving (abrupt-0p5xCO2, 1.97 K). Both forcing and feedback differences explain these climate response differences. Multiple approaches show the radiative forcing for a carbon dioxide doubling is ~10% larger than for a carbon dioxide halving. In addition, radiative feedbacks are less negative in the doubling experiments than in the halving experiments. Specifically, less negative tropical shortwave cloud feedbacks and more positive subtropical cloud feedbacks lead to more greenhouse 2xCO2 warming than 0.5xCO2 greenhouse cooling. Motivated to directly isolate the influence of cloud feedbacks on these experiments, additional abrupt-2xCO2 and abrupt-0p5xCO2 experiments with disabled cloud-climate feedbacks were run. Comparison of these “cloud-locked” simulations with the original “cloud active” simulations shows cloud feedbacks help explain the nonlinear global surface temperature response to greenhouse warming and greenhouse cooling. Overall, these results demonstrate that both radiative forcing and radiative feedbacks are needed to explain differences in the surface climate response to increased and decreased carbon dioxide concentrations.</p>

Influence of Ocean and Atmosphere Components on Simulated Climate Sensitivities

2013 ◽  
Vol 26 (1) ◽  
pp. 231-245 ◽  
Author(s):  
Michael Winton ◽  
Alistair Adcroft ◽  
Stephen M. Griffies ◽  
Robert W. Hallberg ◽  
Larry W. Horowitz ◽  
...  
Keyword(s):  
Sea Ice ◽  
Climate Models ◽  
Climate Model ◽  
Model Simulation ◽  
Coupled Model ◽  
Ocean Model ◽  
Historical Simulation ◽  
Model Version ◽  
Salinity Response ◽  
The Impact

Abstract The influence of alternative ocean and atmosphere subcomponents on climate model simulation of transient sensitivities is examined by comparing three GFDL climate models used for phase 5 of the Coupled Model Intercomparison Project (CMIP5). The base model ESM2M is closely related to GFDL’s CMIP3 climate model version 2.1 (CM2.1), and makes use of a depth coordinate ocean component. The second model, ESM2G, is identical to ESM2M but makes use of an isopycnal coordinate ocean model. The authors compare the impact of this “ocean swap” with an “atmosphere swap” that produces the GFDL Climate Model version 3 (CM3) by replacing the AM2 atmospheric component with AM3 while retaining a depth coordinate ocean model. The atmosphere swap is found to have much larger influence on sensitivities of global surface temperature and Northern Hemisphere sea ice cover. The atmosphere swap also introduces a multidecadal response time scale through its indirect influence on heat uptake. Despite significant differences in their interior ocean mean states, the ESM2M and ESM2G simulations of these metrics of climate change are very similar, except for an enhanced high-latitude salinity response accompanied by temporarily advancing sea ice in ESM2G. In the ESM2G historical simulation this behavior results in the establishment of a strong halocline in the subpolar North Atlantic during the early twentieth century and an associated cooling, which are counter to observations in that region. The Atlantic meridional overturning declines comparably in all three models.

scholarly journals Comparison of Equilibrium Climate Sensitivity Estimates From Slab Ocean, 150‐Year, and Longer Simulations

2020 ◽  
Vol 47 (16) ◽  
Author(s):  
John P. Dunne ◽  
Michael Winton ◽  
Julio Bacmeister ◽  
Gokhan Danabasoglu ◽  
Andrew Gettelman ◽  
...  
Keyword(s):  
Climate Sensitivity ◽  
Equilibrium Climate Sensitivity ◽  
Slab Ocean

scholarly journals The importance of interactive chemistry for stratosphere–troposphere coupling

2019 ◽  
Vol 19 (5) ◽  
pp. 3417-3432 ◽  
Author(s):  
Sabine Haase ◽  
Katja Matthes
Keyword(s):  
Ozone Depletion ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Ocean Model ◽  
Recent Past ◽  
Stratospheric Polar Vortex ◽  
Model Version ◽  
Surface Climate ◽  
The Mean ◽  
Mean State

Abstract. Recent observational and modeling studies suggest that stratospheric ozone depletion not only influences the surface climate in the Southern Hemisphere (SH), but also impacts Northern Hemisphere (NH) spring, which implies a strong interaction between dynamics and chemistry. Here, we systematically analyze the importance of interactive chemistry with respect to the representation of stratosphere–troposphere coupling and in particular the effects on NH surface climate during the recent past. We use the interactive and specified chemistry version of NCAR's Whole Atmosphere Community Climate Model coupled to an ocean model to investigate differences in the mean state of the NH stratosphere as well as in stratospheric extreme events, namely sudden stratospheric warmings (SSWs), and their surface impacts. To be able to focus on differences that arise from two-way interactions between chemistry and dynamics in the model, the specified chemistry model version uses a time-evolving, model-consistent ozone field generated by the interactive chemistry model version. We also test the effects of zonally symmetric versus asymmetric prescribed ozone, evaluating the importance of ozone waves in the representation of stratospheric mean state and variability. The interactive chemistry simulation is characterized by a significantly stronger and colder polar night jet (PNJ) during spring when ozone depletion becomes important. We identify a negative feedback between lower stratospheric ozone and atmospheric dynamics during the breakdown of the stratospheric polar vortex in the NH, which contributes to the different characteristics of the PNJ between the simulations. Not only the mean state, but also stratospheric variability is better represented in the interactive chemistry simulation, which shows a more realistic distribution of SSWs as well as a more persistent surface impact afterwards compared with the simulation where the feedback between chemistry and dynamics is switched off. We hypothesize that this is also related to the feedback between ozone and dynamics via the intrusion of ozone-rich air into polar latitudes during SSWs. The results from the zonally asymmetric ozone simulation are closer to the interactive chemistry simulations, implying that under a model-consistent ozone forcing, a three-dimensional (3-D) representation of the prescribed ozone field is desirable. This suggests that a 3-D ozone forcing, as recommended for the upcoming CMIP6 simulations, has the potential to improve the representation of stratospheric dynamics and chemistry. Our findings underline the importance of the representation of interactive chemistry and its feedback on the stratospheric mean state and variability not only in the SH but also in the NH during the recent past.

Assessing spatio-temporal variability and biases of climate models

2020 ◽  
Author(s):  
Nedjeljka Žagar
Keyword(s):  
Temporal Variability ◽  
Prediction Models ◽  
Climate Model ◽  
Weather Prediction ◽  
Ocean Model ◽  
Spatial And Temporal Variability ◽  
Dynamical Regime ◽  
Temporal Variance ◽  
Slab Ocean ◽  
Spatio Temporal

<div>Atmospheric spatial and temporal variability are closely related with the former being relatively well observed compared to the latter. The former is also regularly assessed in the validation of numerical weather prediction models while the latter is more difficult to estimate. Likewise, thermodynamical fields and circulation are closely coupled calling for an approach that considers them simultaneously.  </div> <div>In this contribution, spatio-temporal variability spectra of the four major reanalysis datasets are discussed and applied for the validation of a climate model prototype.  A relationship between deficiencies in simulated variability and model biases is derived. The underlying method includes dynamical regime decomposition thereby providing a better understanding of the role of tropical variability in global circulation. </div> <div>Results of numerical simulations are validated by a 20th century reanalysis. A climate model was forced either with the prescribed SST or with a slab ocean model that updates SST in each forecast step.  Scale-dependent validation shows that missing temporal variance in the model relative to verifying reanalysis increases as the spatial scale reduces that appears associated with an increasing lack of spatial variance at smaller scales. Similar to variability, bias is strongly scale dependent; the larger the scale, the greater the bias. Biases present in the SST-forced simulation increase in the simulation using the slab ocean. The comparison of biases computed as a systematic difference between the model and reanalysis and between the SST-forced model and slab-ocean model (a perfect-model scenario) suggests that improving the atmospheric model increases the variance in the model on synoptic and subsynoptic scales but large biases associated with a poor SST remain at planetary scales.</div> <p> </p>

scholarly journals EMPIRICALLY CONSTRAINED CLIMATE SENSITIVITY AND THE SOCIAL COST OF CARBON

2017 ◽  
Vol 08 (02) ◽  
pp. 1750006 ◽  
Author(s):  
KEVIN DAYARATNA ◽  
ROSS McKITRICK ◽  
DAVID KREUTZER
Keyword(s):  
Climate Sensitivity ◽  
Integrated Assessment ◽  
Social Cost ◽  
Climate Model ◽  
Temperature Response ◽  
Social Cost Of Carbon ◽  
Ocean Heat Uptake ◽  
Monte Carlo Experiments ◽  
The Social ◽  
Dice Model

Integrated Assessment Models (IAMs) require parameterization of both economic and climatic processes. The latter includes Equilibrium Climate Sensitivity (ECS), or the temperature response to doubling CO2 levels, and Ocean Heat Uptake (OHU) efficiency. ECS distributions in IAMs have been drawn from climate model runs that lack an empirical basis, and in Monte Carlo experiments may not be constrained to consistent OHU values. Empirical ECS estimates are now available, but have not yet been applied in IAMs. We incorporate a new estimate of the ECS distribution conditioned on observed OHU efficiency into two widely used IAMs. The resulting Social Cost of Carbon (SCC) estimates are much lower than those from models based on simulated ECS parameters. In the DICE model, the average SCC falls by approximately 40–50% depending on the discount rate, while in the FUND model the average SCC falls by over 80%. The span of estimates across discount rates also shrinks substantially.

scholarly journals Decadal Prediction of the Sahelian Precipitation in CMIP5 Simulations

2013 ◽  
Vol 26 (19) ◽  
pp. 7708-7719 ◽  
Author(s):  
Marco Gaetani ◽  
Elsa Mohino
Keyword(s):  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Coupled Model ◽  
System Model ◽  
Low Resolution ◽  
Coupled Models ◽  
Climate System Model ◽  
Model Version ◽  
Coupled Global Climate Model

Abstract In this study the capability of eight state-of-the-art ocean–atmosphere coupled models in predicting the monsoonal precipitation in the Sahel on a decadal time scale is assessed. To estimate the importance of the initialization, the predictive skills of two different CMIP5 experiments are compared, a set of 10 decadal hindcasts initialized every 5 years in the period 1961–2009 and the historical simulations in the period 1961–2005. Results indicate that predictive skills are highly model dependent: the Fourth Generation Canadian Coupled Global Climate Model (CanCM4), Centre National de Recherches Météorologiques Coupled Global Climate Model, version 5 (CNRM-CM5), and Max Planck Institute Earth System Model, low resolution (MPI-ESM-LR) models show improved skill in the decadal hindcasts, while the Model for Interdisciplinary Research on Climate, version 5 (MIROC5) is skillful in both the decadal and historical experiments. The Beijing Climate Center, Climate System Model, version 1.1 (BCC-CSM1.1), Hadley Centre Coupled Model, version 3 (HadCM3), L'Institut Pierre-Simon Laplace Coupled Model, version 5, coupled with NEMO, low resolution (IPSL-CM5A-LR), and Meteorological Research Institute Coupled Atmosphere–Ocean General Circulation Model, version 3 (MRI-CGCM3) models show insignificant or no skill in predicting the Sahelian precipitation. Skillful predictions are produced by models properly describing the SST multidecadal variability and the initialization appears to play an important role in this respect.

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