This paper describes the main characteristics of CNRM‐CM6‐1, the fully coupled atmosphere‐ocean general circulation model of sixth generation jointly developed by Centre National de Recherches ...Météorologiques (CNRM) and Cerfacs for the sixth phase of the Coupled Model Intercomparison Project 6 (CMIP6). The paper provides a description of each component of CNRM‐CM6‐1, including the coupling method and the new online output software. We emphasize where model's components have been updated with respect to the former model version, CNRM‐CM5.1. In particular, we highlight major improvements in the representation of atmospheric and land processes. A particular attention has also been devoted to mass and energy conservation in the simulated climate system to limit long‐term drifts. The climate simulated by CNRM‐CM6‐1 is then evaluated using CMIP6 historical and Diagnostic, Evaluation and Characterization of Klima (DECK) experiments in comparison with CMIP5 CNRM‐CM5.1 equivalent experiments. Overall, the mean surface biases are of similar magnitude but with different spatial patterns. Deep ocean biases are generally reduced, whereas sea ice is too thin in the Arctic. Although the simulated climate variability remains roughly consistent with CNRM‐CM5.1, its sensitivity to rising CO2 has increased: the equilibrium climate sensitivity is 4.9 K, which is now close to the upper bound of the range estimated from CMIP5 models.
Key Points
Description of CNRM‐CM6‐1 model components, their coupling, and tuning procedures are described
Historical simulations and DECK experiments are assessed
Preindustrial simulation is stable and mean climate and variability in historical runs is realistic
Characteristics and radiative forcing of the aerosol and ozone fields of two configurations of the Centre National de Recherches Météoroglogiques (CNRM) and Cerfacs climate model are analyzed over ...the historical period (1850–2014), using several Coupled Model Intercomparison Project 6 (CMIP6) simulations. CNRM‐CM6‐1 is the atmosphere‐ocean general circulation model including prescribed aerosols and a linear stratospheric ozone scheme, while the Earth System Model CNRM‐ESM2‐1 has interactive tropospheric aerosols and chemistry of the midtroposphere aloft. The representations of aerosols and ozone in CNRM‐CM6‐1 are issued from simulations of CNRM‐ESM2‐1, and this ensures some comparability of both representations. In particular, present‐day anthropogenic aerosol optical depths are similar (0.018), and their spatial patterns correspond to those of reference data sets such as MACv2 and MACv2‐SP despite a negative bias. Effective radiative forcings (ERFs) have been estimated using 30‐year fixed sea surface temperature simulations (piClim) and several calls to the radiative scheme. Present‐day anthropogenic aerosol ERF, aerosol‐radiation ERF, and aerosol cloud ERF are fully within CMIP5 estimates and, respectively, equal to
−1.10,
−0.36, and
−0.81 W m
−2 for CNRM‐CM6‐1 and
−0.21,
−0.61, and
−0.74 W m
−2 for CNRM‐ESM2‐1. Additional CMIP6‐type piClim simulations show that these differences are mainly due to the interactivity of the aerosol scheme whose impact is confirmed when assessing the response of both climate model configurations to rising CO
2. Present‐day stratospheric ozone ERF, equal to
−0.04 W m
−2, is in agreement with that of the CMIP6 ozone. No trend appears in the ozone ERF over the historical period although the evolution of the total column ozone is correctly simulated.
Plain Language Summary
The manuscript documents the Météo‐France Centre National de Recherches Météorologiques aerosol‐chemistry modeling contributions to the sixth Coupled Model Intercomparison Project that supports the sixth IPCC Assessment Report of climate change. It establishes that their results are suitable for use by the scientific community in the analysis of the sixth Coupled Model Intercomparison Project experiments. The authors provide an evaluation of the model performance in both present‐day and historical (1850–2014) contexts, as well as a detailed analysis of the model calculated effective radiative forcing due to ozone and aerosols.
Key Points
The representations of aerosol and ozone in the CMIP6 CNRM‐CM6‐1 and CNRM‐ESM2‐1 models is described
Present‐day and historical aerosol and ozone distributions are assessed, as well as their effective radiative forcing (ERF)
The present‐day anthropogenic aerosol ERF (‐1.10 W m
−2 for CNRM‐CM6‐1) is sensitive to the interactivity of aerosols
Captive large felines are prone to abnormal repetitive behaviors like pacing, which are associated with welfare issues. Visual contact without the opportunity to engage in appropriate behavior is ...known to increase pacing. To better understand the relationship between pacing and conspecific visual contact, we investigated this effect by conducting a barrier experiment on a male‐female pair of Sumatran tigers (Panthera tigris sumatrae) in Rotterdam Zoo, the Netherlands. The tigers were exposed to four consecutive housing treatments: (i) housed in the same enclosure (baseline), (ii) housed in separate enclosures with visual contact, (iii) housed in separate enclosures without visual contact, and (iv) housed in the same enclosure after the separation. We used focal and scan sampling to measure pacing and recorded the number of visitors. Moreover, we applied scan sampling to measure activity. Overall, our results indicate that the tigers paced significantly more when housed in separate enclosures with conspecific visual contact. Moreover, our results suggest that limiting visual contact between neighboring tigers can mitigate pacing. Implementing these findings in tiger husbandry and enclosure design has the potential to improve animal welfare zoo populations of large felines.
Pacing in neighboring tigers significantly decreases when visual contact between the animals is avoided.
Research highlights
Limiting visual contact mitigated pacing in a tiger pair when housed in separate zoo enclosures.
Implementing this information in zoo husbandry potentially improves the welfare of tigers and other large felines.
We have implemented a prognostic aerosol scheme (v1) in CNRM-CM6, the climate model of CNRM-GAME and CERFACS, based upon the GEMS/MACC aerosol module of the ECMWF operational forecast model. This ...scheme describes the physical evolution of the five main types of aerosols, namely black carbon, organic matter, sulfate, desert dust and sea salt. In this work, we describe the characteristics of our implementation, for instance, taking into consideration a different dust scheme or boosting biomass burning emissions by a factor of 2, as well as the evaluation performed on simulation output. The simulations consist of time slice simulations for 2004 conditions and transient runs over the 1993–2012 period, and are either free-running or nudged towards the ERA-Interim Reanalysis. Evaluation data sets include several satellite instrument AOD (aerosol optical depth) products (i.e., MODIS Aqua classic and Deep-Blue products, MISR and CALIOP products), as well as ground-based AERONET data and the derived AERONET climatology, MAC-v1. The uncertainty of aerosol-type seasonal AOD due to model internal variability is low over large parts of the globe, and the characteristics of a nudged simulation reflect those of a free-running simulation. In contrast, the impact of the new dust scheme is large, with modelled dust AODs from simulations with the new dust scheme close to observations. Overall patterns and seasonal cycles of the total AOD are well depicted with, however, a systematic low bias over oceans. The comparison to the fractional MAC-v1 AOD climatology shows disagreements mostly over continents, while that to AERONET sites outlines the capability of the model to reproduce monthly climatologies under very diverse dominant aerosol types. Here again, underestimation of the total AOD appears in several cases, sometimes linked to insufficient efficiency of the aerosol transport away from the aerosol sources. Analysis of monthly time series at 166 AERONET sites shows, in general, correlation coefficients higher than 0.5 and lower model variance than observed. A large interannual variability can also be seen in the CALIOP vertical profiles over certain regions of the world. Overall, this prognostic aerosol scheme appears promising for aerosol-climate studies. There is room, however, for implementing more complex parameterisations in relation to aerosols.
The impact of stratospheric ozone on the tropospheric general circulation of the Southern Hemisphere (SH) is examined with a set of chemistry‐climate models participating in the Stratospheric ...Processes and their Role in Climate (SPARC)/Chemistry‐Climate Model Validation project phase 2 (CCMVal‐2). Model integrations of both the past and future climates reveal the crucial role of stratospheric ozone in driving SH circulation change: stronger ozone depletion in late spring generally leads to greater poleward displacement and intensification of the tropospheric midlatitude jet, and greater expansion of the SH Hadley cell in the summer. These circulation changes are systematic as poleward displacement of the jet is typically accompanied by intensification of the jet and expansion of the Hadley cell. Overall results are compared with coupled models participating in the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4), and possible mechanisms are discussed. While the tropospheric circulation response appears quasi‐linearly related to stratospheric ozone changes, the quantitative response to a given forcing varies considerably from one model to another. This scatter partly results from differences in model climatology. It is shown that poleward intensification of the westerly jet is generally stronger in models whose climatological jet is biased toward lower latitudes. This result is discussed in the context of quasi‐geostrophic zonal mean dynamics.
Substantial increases in the atmospheric concentration of well‐mixed greenhouse gases (notably CO2), such as those projected to occur by the end of the 21st century under large radiative forcing ...scenarios, have long been known to cause an acceleration of the Brewer‐Dobson circulation (BDC) in climate models. More recently, however, several single‐model studies have proposed that ozone‐depleting substances might also be important drivers of BDC trends. As these studies were conducted with different forcings over different periods, it is difficult to combine them to obtain a robust quantitative picture of the relative importance of ozone‐depleting substances as drivers of BDC trends. To this end, we here analyze—over identical past and future periods—the output from 20 similarly forced models, gathered from two recent chemistry‐climate modeling intercomparison projects. Our multimodel analysis reveals that ozone‐depleting substances are responsible for more than half of the modeled BDC trends in the two decades 1980–2000. We also find that, as a consequence of the Montreal Protocol, decreasing concentrations of ozone‐depleting substances in coming decades will strongly decelerate the BDC until the year 2080, reducing the age‐of‐air trends by more than half, and will thus substantially mitigate the impact of increasing CO2. As ozone‐depleting substances impact BDC trends, primarily, via the depletion/recovery of stratospheric ozone over the South Pole, they impart seasonal and hemispheric asymmetries to the trends which may offer opportunities for detection in coming decades.
Key Points
Impacts of ozone‐depleting substances (ODS) on Brewer‐Dobson circulation trends are analyzed in 20 chemistry‐climate models
For the period 1980–2000 ODS have contributed more than half (roughly 60%) of the stratospheric age‐of‐air trends
For the period 2000–2080 models show that decreasing ODS levels will substantially decelerate the BDC
The goal of the Chemistry‐Climate Model Validation (CCMVal) activity is to improve understanding of chemistry‐climate models (CCMs) through process‐oriented evaluation and to provide reliable ...projections of stratospheric ozone and its impact on climate. An appreciation of the details of model formulations is essential for understanding how models respond to the changing external forcings of greenhouse gases and ozone‐depleting substances, and hence for understanding the ozone and climate forecasts produced by the models participating in this activity. Here we introduce and review the models used for the second round (CCMVal‐2) of this intercomparison, regarding the implementation of chemical, transport, radiative, and dynamical processes in these models. In particular, we review the advantages and problems associated with approaches used to model processes of relevance to stratospheric dynamics and chemistry. Furthermore, we state the definitions of the reference simulations performed, and describe the forcing data used in these simulations. We identify some developments in chemistry‐climate modeling that make models more physically based or more comprehensive, including the introduction of an interactive ocean, online photolysis, troposphere‐stratosphere chemistry, and non‐orographic gravity‐wave deposition as linked to tropospheric convection. The relatively new developments indicate that stratospheric CCM modeling is becoming more consistent with our physically based understanding of the atmosphere.
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