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1. Equilibrium- and Transient-State Dependencies of Climate Sensitivity: Are They Important for Climate Projections?

Author

David Saint-Martin and Olivier Geoffroy

Subjects
Atmospheric Science, Transient state, 010504 meteorology & atmospheric sciences, Climatology, Environmental science, Climate sensitivity, Climate change, Climate model, 010502 geochemistry & geophysics, Constant (mathematics), 01 natural sciences, 0105 earth and related environmental sciences
Abstract

The effective equilibrium climate sensitivity is generally assumed to be constant in climate change studies, whereas it may vary due to different mechanisms. This study assesses the importance of the different types of state dependencies of the radiative feedbacks for constraining climate projections from the historical record. In transition, the radiative feedbacks may vary with the changes in the warming pattern due to inhomogeneous ocean heat uptake. They may also vary in equilibrium due to their dependence on both temperature and CO2 concentration. A two-layer energy balance model (EBM) that accounts for these effects is shown to improve the representation of any CO2 pathway for the CMIP5 ensemble. Neglecting the nonlinear effects in constraint studies of climate projections from the historical record may induce errors in the estimated future warming. The EBM framework is used to study these errors for three characteristic CO2 pathways. The results show that the pattern effect of ocean heat uptake is not of major importance by inducing a median error of roughly −2% for a high-emission scenario. In contrast, assuming a log-linear CO2–ERF relationship and neglecting the equilibrium-state dependencies induce a larger median error of roughly −10%. This median error is likely due to the non-log-linear dependency of the instantaneous (nonadjusted) forcing, suggesting that the equilibrium-state dependencies do not induce any systematic error. However, they contribute to increasing uncertainties in future warming estimation.

Published
2020

2. Tracking Changes in Climate Sensitivity in CNRM Climate Models

Author

David Saint-Martin, Hervé Douville, Jean-François Guérémy, Aurore Voldoire, Laurent Terray, Bertrand Decharme, Julien Cattiaux, Sophie Valcke, Christine Delire, Romain Roehrig, Emilie Joetzjer, Matthieu Chevallier, Jeanne Colin, Aurélien Ribes, Fabrice Chauvin, Olivier Geoffroy, Florent Brient, Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Centre Européen de Biotechnologies et Bioéconomie (CEBB), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS-PSL), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL)

Subjects
Physical geography, 010504 meteorology & atmospheric sciences, Climate change, GC1-1581, 010502 geochemistry & geophysics, global warming, Oceanography, 01 natural sciences, Cloud feedback, climate models, Radiative transfer, Environmental Chemistry, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Global and Planetary Change, Global warming, Longwave, GB3-5030, 13. Climate action, [SDU]Sciences of the Universe [physics], [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, Climatology, [SDE]Environmental Sciences, General Earth and Planetary Sciences, Environmental science, Climate sensitivity, climate sensitivity, Climate model, Shortwave
Abstract

International audience; The equilibrium climate sensitivity (ECS) in the latest version of CNRM climate model, CNRM-CM6-1, and in its high-resolution counterpart, CNRM-CM6-1-HR, is significantly larger than in the previous version (CNRM-CM5.1). The traceability of this climate sensitivity change is investigated using coupled ocean-atmosphere model climate change simulations. These simulations show that the increase in ECS is the result of changes in the atmospheric component. A particular attention is paid to the method used to decompose the equilibrium temperature response difference, by using a linearized decomposition of the individual radiative agents diagnosed by a radiative kernel technique. The climate sensitivity increase is primarily due to the cloud radiative responses, with a predominant contribution of the tropical longwave response (including both feedback and forcing adjustment) and a significant contribution of the extratropical and tropical shortwave feedback changes. A series of stand-alone atmosphere experiments is carried out to quantify the contributions of each atmospheric development to this difference between CNRM-CM5.1 and CNRM-CM6-1. The change of the convection scheme appears to play an important role in driving the cloud changes, with a large effect on the tropical longwave cloud feedback change.

Published
2021

3. Equilibrium climate sensitivity estimated by equilibrating climate models

Author

Chao Li, Long Cao, Maria Rugenstein, Gavin A. Schmidt, Olivier Geoffroy, Thorsten Mauritsen, Timothy Andrews, Shuting Yang, Gokhan Danabasoglu, Thomas L. Frölicher, Jonathan M. Gregory, Jean-Louis Dufresne, David Paynter, Reto Knutti, Jonah Bloch-Johnson, Ayako Abe-Ouchi, Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institute for Atmospheric and Climate Science [Zürich] (IAC), Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich] (ETH Zürich), Max Planck Institute for Meteorology (MPI-M), Max-Planck-Gesellschaft, NCAS-Climate [Reading], Department of Meteorology [Reading], University of Reading (UOR)-University of Reading (UOR), Met Office Hadley Centre for Climate Change (MOHC), United Kingdom Met Office [Exeter], Department of Meteorology [Stockholm] (MISU), Stockholm University, Climate and Environmental Physics [Bern] (CEP), Physikalisches Institut [Bern], Universität Bern [Bern]-Universität Bern [Bern], Oeschger Centre for Climate Change Research (OCCR), University of Bern, National Center for Atmospheric Research [Boulder] (NCAR), NOAA Geophysical Fluid Dynamics Laboratory (GFDL), National Oceanic and Atmospheric Administration (NOAA), Danish Meteorological Institute (DMI), Département des Géosciences - ENS Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École des Ponts ParisTech (ENPC)-École polytechnique (X)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), School of Earth Sciences, Zhejiang University (ZJU), NASA Goddard Institute for Space Studies (GISS), NASA Goddard Space Flight Center (GSFC), Atmosphere and Ocean Research Institute [Kashiwa-shi] (AORI), The University of Tokyo (UTokyo), Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Department of Psychology [York, UK], University of York [York, UK], State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Center for Climate System Research [Kashiwa] (CCSR), and Royal Netherlands Meteorological Institute (KNMI)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010504 meteorology & atmospheric sciences, 530 Physics, Extrapolation, Geovetenskap och miljövetenskap, [SDU.STU.ME]Sciences of the Universe [physics]/Earth Sciences/Meteorology, 010502 geochemistry & geophysics, Atmospheric sciences, 01 natural sciences, Geophysics, 13. Climate action, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, General Circulation Model, Radiative transfer, Range (statistics), Spatial ecology, General Earth and Planetary Sciences, Environmental science, Climate sensitivity, Climate model, Earth and Related Environmental Sciences, ComputingMilieux_MISCELLANEOUS, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences
Abstract

The methods to quantify equilibrium climate sensitivity are still debated. We collect millennial‐length simulations of coupled climate models and show that the global mean equilibrium warming is higher than those obtained using extrapolation methods from shorter simulations. Specifically, 27 simulations with 15 climate models forced with a range of CO2 concentrations show a median 17% larger equilibrium warming than estimated from the first 150 years of the simulations. The spatial patterns of radiative feedbacks change continuously, in most regions reducing their tendency to stabilizing the climate. In the equatorial Pacific, however, feedbacks become more stabilizing with time. The global feedback evolution is initially dominated by the tropics, with eventual substantial contributions from the mid‐latitudes. Time‐dependent feedbacks underscore the need of a measure of climate sensitivity that accounts for the degree of equilibration, so that models, observations, and paleo proxies can be adequately compared and aggregated to estimate future warming.\ud \ud \ud Key points\ud \ud \ud \ud 27 simulations of 15 general circulation models are integrated to near equilibrium\ud All models simulate a higher equilibrium warming than predicted by using extrapolation methods\ud Tropics and mid‐latitudes dominate the change of the feedback parameter on different timescales on millennial timescales

Published
2020

4. LongRunMIP: Motivation and design for a large collection of millennial-length AOGCM simulations

Author

Thomoas Frölicher, David Paynter, Jonathan M. Gregory, David Saint-Martin, Jean-Louis Dufresne, Thorsten Mauritsen, Maria Rugenstein, Tarun Chadha, Ayako Abe-Ouchi, Matthew Menary, Elisabeth J. Moyer, Timothy Andrews, Lei Duan, Larissa Nazarenko, Chao Li, Olivier Geoffroy, Shuting Yang, Gavin A. Schmidt, Gokhan Danabasoglu, Long Cao, Jonah Bloch-Johnson, Marie-Alice Foujols, Urs Beyerle, Akitomo Yamamoto, Reto Knutti, and Alice Marzocchi

Subjects
Atmospheric Science, 010504 meteorology & atmospheric sciences, Mathematical model, 530 Physics, Geovetenskap och miljövetenskap, Representation (systemics), Last Glacial Maximum, 010502 geochemistry & geophysics, 01 natural sciences, Physics::Geophysics, 13. Climate action, Climatology, Environmental science, Climate sensitivity, Climate model, Earth and Related Environmental Sciences, 550 Earth sciences & geology, 0105 earth and related environmental sciences
Abstract

LongRunMIP is the first collection of millennial-length simulations of complex coupled climate models and enables investigations of how these models equilibrate in response to radiative perturbations.\ud \ud We present a model intercomparison project, LongRunMIP, the first collection of millennial-length (1000+ year) simulations of complex coupled climate models with a representation of ocean, atmosphere, sea ice, and land surface, and their interactions. Standard model simulations are generally only a few hundred years long. However, modeling the long-term equilibration in response to radiative forcing perturbation is important for understanding many climate phenomena, such as the evolution of ocean circulation, time-and temperature-dependent feedbacks, and the differentiation of forced signal and internal variability. The aim of LongRunMIP is to facilitate research into these questions by serving as an archive for simulations that capture as much of this equilibration as possible. The only requirement to participate in LongRunMIP is to contribute a simulation with elevated, constant CO2 forcing that lasts at least 1000 years. LongRunMIP is a MIP of opportunity in that the simulations were mostly performed prior to the conception of the archive without an agreed-upon set of experiments. For most models, the archive contains a preindustrial control simulation and simulations with an idealized (typically abrupt) CO2 forcing. We collect 2D surface and top-of-atmosphere fields, and 3D ocean temperature and salinity fields. Here, we document the collection of simulations and discuss initial results, including the evolution of surface and deep ocean temperature and cloud radiative effects. As of summer 2019, the collection includes 50 simulations of 15 models by 10 modeling centers. The data of LongRunMIP are publicly available. We encourage submission of more simulations in the future.

Published
2020
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5. Assessing the Robustness of Future Extreme Precipitation Intensification in the CMIP5 Ensemble

Author

Olivier Geoffroy, Markus G. Donat, Margot Bador, and Lisa V. Alexander

Subjects
Wet season, Atmospheric Science, 010504 meteorology & atmospheric sciences, 0208 environmental biotechnology, Extreme events, Tropics, Climate change, 02 engineering and technology, 15. Life on land, 01 natural sciences, 020801 environmental engineering, 13. Climate action, Climatology, Dry season, Environmental science, Climate model, Precipitation, Robustness (economics), 0105 earth and related environmental sciences
Abstract

A warming climate is expected to intensify extreme precipitation, and climate models project a general intensification of annual extreme precipitation in most regions of the globe throughout the twenty-first century. We investigate the robustness of this future intensification over land across different models, regions, and seasons and evaluate the role of model interdependencies in the CMIP5 ensemble. Strong similarities in extreme precipitation changes are found between models that share atmospheric physics, turning an ensemble of 27 models into around 14 projections. We find that future annual extreme precipitation intensity increases in the majority of models and in the majority of land grid cells, from the driest to the wettest regions, as defined by each model’s precipitation climatology. The intermodel spread is generally larger over wet than over dry regions, smaller in the dry season compared to the wet season and at the annual scale, and largely reduced in extratropical compared to tropical regions and at the global scale. For each model, the future increase in annual and seasonal maximum daily precipitation amounts exceeds the range of simulated internal variability in the majority of land grid cells. At both annual and seasonal scales, however, there are a few regions where the change is still within the background climate noise, but their size and location differ between models. In extratropical regions, the signal-to-noise ratio of projected changes in extreme precipitation is particularly robust across models because of a similar change and background climate noise, whereas projected changes are less robust in the tropics.

Published
2018

6. The Role of Nonlinear Drying above the Boundary Layer in the Mid-Holocene African Monsoon

Author

Steven C. Sherwood, Olivier Geoffroy, Damianos Mantsis, and Vishal Dixit

Subjects
Atmospheric Science, 010504 meteorology & atmospheric sciences, Orbital forcing, Atmospheric circulation, Northern Hemisphere, 15. Life on land, 010502 geochemistry & geophysics, Monsoon, Atmospheric sciences, 01 natural sciences, Boundary layer, 13. Climate action, Climatology, Climate model, Precipitation, Holocene, Geology, 0105 earth and related environmental sciences
Abstract

Paleoclimatic proxies indicate that significant summertime rainfall reached the Sahara region during the mid-Holocene, presumably in response to stronger summertime heating in the Northern Hemisphere. Climate models generally do not replicate the enhanced precipitation. As a step toward understanding the response and possible role of model errors, a series of idealized experiments were conducted with the Community Earth System Model in which local atmospheric heat sources of increasing magnitude were applied in the boundary layer over the Sahel and Sahara. In response to this local heating, the cold and moist southwesterly monsoon inflow encroaches farther northward. A source strength of roughly 1 K day−1 produces responses similar to those in a simulation with mid-Holocene orbital forcing imposed globally, while that of 1.5 K day−1 produces a precipitation response similar to that from paleoproxies. The precipitation increases nonlinearly, with a jump at heating of around 1 K day−1, even though the low-level monsoon inflow increases linearly. Competition at low-to-middle levels between drying by a shallow return flow just above the boundary layer and moistening by vertical advection within the layer affects convection and determines the northward extension of precipitation. When the heating becomes 1.5 K day−1, the boundary layer flow encroaches sufficiently northward to weaken the shallow return flow, further aiding precipitation. This novel nonlinear mechanism operates without biogeophysical feedbacks, and suggests that poor representation of the local thermodynamic processes may hamper a model’s ability to simulate dynamical feedbacks and hence the strength and poleward extension of monsoon rains under forcings like those during the mid-Holocene.

Published
2017

7. On the role of the stratiform cloud scheme in the inter‐model spread of cloud feedback

Author

Olivier Geoffroy, David Fuchs, and Steven C. Sherwood

Subjects
Global and Planetary Change, 010504 meteorology & atmospheric sciences, Meteorology, business.industry, Probability density function, Cloud computing, 010502 geochemistry & geophysics, Atmospheric sciences, 01 natural sciences, Cloud feedback, Stability (probability), Negative feedback, General Earth and Planetary Sciences, Environmental Chemistry, Environmental science, Climate sensitivity, Climate model, business, Astrophysics::Galaxy Astrophysics, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences, Positive feedback
Abstract

This study explores the role of the stratiform cloud scheme in the inter-model spread of cloud feedback. Six diagnostic cloud schemes used in various CMIP (Coupled Model Intercomparison Experiment] climate models are implemented (at low and midlevels) into two testbed climate models, and the impacts on cloud feedback are investigated. Results suggest that the choice of stratiform cloud scheme may contribute up to roughly half of the intermodel spread of cloud radiative responses in stratocumulus (Sc) regions, and may determine or favor a given sign of the feedback there. Cloud schemes assuming a probability density function for total water content consistently predict a positive feedback in Sc regions in our experiments. A large negative feedback in Sc regions is obtained only with schemes that consider variables other than relative humidity (e.g., stability). The stratiform cloud scheme also significantly affects cloud feedback at the scale of the tropics and at global scale. Results are slightly less consistent for tropical means, likely indicating coupling with other boundary layer processes such as convective mixing.

Published
2017

8. Fast‐Forward to Perturbed Equilibrium Climate

Author

David Saint-Martin, Olivier Geoffroy, Bertrand Decharme, Aurore Voldoire, Aurélien Ribes, Julien Cattiaux, L. Watson, Hervé Douville, Gilles Bellon, Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), University of Auckland [Auckland], Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), and Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010504 meteorology & atmospheric sciences, Global warming, Radiative forcing, 010502 geochemistry & geophysics, 7. Clean energy, 01 natural sciences, Geophysics, 13. Climate action, Climatology, General Earth and Planetary Sciences, Environmental science, Climate sensitivity, Climate model, 0105 earth and related environmental sciences
Abstract

International audience; The equilibrium climate sensitivity, that is, the global-mean surface-air temperature change in response to a doubling of the carbon dioxide concentration is a widely used metric in climate change studies. Its exact value is rarely known because its estimation requires a long integration time of several thousand years. We propose a method to estimate an accurate value of the equilibrium response from fully coupled climate models at a reasonable computational cost. Using this method, our state-of-the-art climate model CNRM-CM6-1 reaches a stationary state after only few hundred of years of integration. This "Fast-Forward" method consists of an optimal two-step forcing pathway designed using the framework of a two-layer energy balance model. It can be applied easily to any coupled climate model.

Published
2019

9. Evaluation of CMIP6 DECK Experiments With CNRM‐CM6‐1

Author

David Saint-Martin, Yann Meurdesoif, Julie Deshayes, Sophie Belamari, D. Salas y Melia, Robin Waldman, Stephane Sénési, Jeanne Colin, Sophie Valcke, Gurvan Madec, Roland Séférian, Olivier Geoffroy, Hervé Douville, Romain Roehrig, Pierre Nabat, Matthieu Chevallier, Laurent Franchistéguy, Jean-François Guérémy, Sarah Berthet, Christophe Cassou, I. Beau, Bertrand Decharme, Julien Cattiaux, Antoinette Alias, M. P. Moine, Rym Msadek, Emilia Sanchez-Gomez, Christian Ethé, C. Lévy, Aurélien Ribes, Aurore Voldoire, Laurent Terray, Martine Michou, Groupe de Météorologie de Grande Échelle et Climat (GMGEC), Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Nucleus for European Modeling of the Ocean (NEMO R&D ), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), ANR-13-MONU-0008,CONVERGENCE,Convergence en Science du Climat à l'ère du Big Data et des challenges de l'Exascale.(2013), European Project: 641816,H2020,H2020-SC5-2014-two-stage,CRESCENDO(2015), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), CERFACS, Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)

Subjects
010504 meteorology & atmospheric sciences, Magnitude (mathematics), climate model, 010502 geochemistry & geophysics, 01 natural sciences, lcsh:Oceanography, CMIP6 DECK, Range (statistics), Sea ice, Environmental Chemistry, lcsh:GC1-1581, 14. Life underwater, Sensitivity (control systems), lcsh:Physical geography, 0105 earth and related environmental sciences, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Global and Planetary Change, Coupled model intercomparison project, geography, geography.geographical_feature_category, CNRM‐CM6‐1, 13. Climate action, Climatology, Spatial ecology, General Earth and Planetary Sciences, Environmental science, Climate sensitivity, Climate model, lcsh:GB3-5030
Abstract

International audience; 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 CO 2 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.

Published
2019

10. Evaluation of CNRM Earth‐System model, CNRM‐ESM 2‐1: role of Earth system processes in present‐day and future climate

Author

Sophie Valcke, Marie-Pierre Moine, Christine Delire, Jeanne Colin, Julie Deshayes, Marc Mallet, Laurent Franchistéguy, David Saint-Martin, Gurvan Madec, Matthieu Chevallier, Olivier Geoffroy, Emilie Joetzjer, Robin Waldman, Pierre Nabat, Matthias Rocher, Christian Ethé, Aurore Voldoire, Aurélien Ribes, Roland Séférian, Stephane Sénési, Martine Michou, Laurent Terray, Jessica Vial, Olivier Aumont, Romain Roehrig, David Salas-y-Mélia, Emilia Sanchez, Rym Msadek, Sarah Berthet, Jean-François Guérémy, Laurent Bopp, Bertrand Decharme, Groupe de Météorologie de Grande Échelle et Climat (GMGEC), Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Climat, Environnement, Couplages et Incertitudes [Toulouse] (CECI), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Nucleus for European Modeling of the Ocean (NEMO R&D ), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), H2020 CONSTRAIN under the grant agreement 820829, LEFE CYBER/GMMC PISCO project, ANR-13-MONU-0008,CONVERGENCE,Convergence en Science du Climat à l'ère du Big Data et des challenges de l'Exascale.(2013), European Project: 641816,H2020,H2020-SC5-2014-two-stage,CRESCENDO(2015), Groupe d'étude de l'atmosphère météorologique (CNRM-GAME), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Météo France-Centre National de la Recherche Scientifique (CNRS), Laboratoire Géomatériaux et Environnement (LGE), Université Paris-Est Marne-la-Vallée (UPEM), CAS-PHABIO, Institut de Physique Nucléaire de Lyon (IPNL), Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Météo France, Université Pierre et Marie Curie - Paris 6 (UPMC), Laboratoire d'aérologie (LA), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP)-Université Toulouse III - Paul Sabatier (UPS), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées, Laboratoire de Génie Electrique de Grenoble (G2ELab), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut Polytechnique de Grenoble - Grenoble Institute of Technology-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA), Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Politecnico di Torino [Torino] (Polito), CERFACS, Laboratoire de physique des océans (LPO), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS), Department of Physical Oceanography, Woods Hole Oceanographic Institution (WHOI), Institut Pierre-Simon-Laplace (IPSL), École normale supérieure - Paris (ENS Paris)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National d'Études Spatiales [Toulouse] (CNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), CERFACS-Centre National de la Recherche Scientifique (CNRS), Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)

Subjects
010504 meteorology & atmospheric sciences, Forcing (mathematics), Present day, [SDU.STU.ME]Sciences of the Universe [physics]/Earth Sciences/Meteorology, 010502 geochemistry & geophysics, Atmospheric sciences, 01 natural sciences, Carbon cycle, lcsh:Oceanography, Environmental Chemistry, Earth system modeling, lcsh:GC1-1581, [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, lcsh:Physical geography, climate modeling, CMIP6, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Global and Planetary Change, Coupled model intercomparison project, Vegetation, biogeochemical cycles, 15. Life on land, Earth system science, 13. Climate action, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, Atmospheric chemistry, General Earth and Planetary Sciences, Environmental science, Climate model, future projections, lcsh:GB3-5030, aerosols
Abstract

International audience This study introduces CNRM‐ESM2‐1, the Earth system (ES) model of second generation developed by CNRM‐CERFACS for the sixth phase of the Coupled Model Intercomparison Project (CMIP6). CNRM‐ESM2‐1 offers a higher model complexity than the Atmosphere‐Ocean General Circulation Model CNRM‐CM6‐1 by adding interactive ES components such as carbon cycle, aerosols, and atmospheric chemistry. As both models share the same code, physical parameterizations, and grid resolution, they offer a fully traceable framework to investigate how far the represented ES processes impact the model performance over present‐day, response to external forcing and future climate projections. Using a large variety of CMIP6 experiments, we show that represented ES processes impact more prominently the model response to external forcing than the model performance over present‐day. Both models display comparable performance at replicating modern observations although the mean climate of CNRM‐ESM2‐1 is slightly warmer than that of CNRM‐CM6‐1. This difference arises from land cover‐aerosol interactions where the use of different soil vegetation distributions between both models impacts the rate of dust emissions. This interaction results in a smaller aerosol burden in CNRM‐ESM2‐1 than in CNRM‐CM6‐1, leading to a different surface radiative budget and climate. Greater differences are found when comparing the model response to external forcing and future climate projections. Represented ES processes damp future warming by up to 10% in CNRM‐ESM2‐1 with respect to CNRM‐CM6‐1. The representation of land vegetation and the CO2‐water‐stomatal feedback between both models explain about 60% of this difference. The remainder is driven by other ES feedbacks such as the natural aerosol feedback.

Published
2019

11. Land-sea warming contrast: the role of the horizontal energy transport

Author

David Saint-Martin, Olivier Geoffroy, and Aurore Voldoire

Subjects
Atmospheric Science, Sea surface temperature, Climatology, Radiative transfer, Variance (land use), Environmental science, Climate change, Humidity, Climate sensitivity, Climate model, Deep sea
Abstract

In this study we investigate the role of the mechanisms at play in the magnitude of the land-sea warming contrast and its intermodel spread in the fifth coupled models intercomparison project (CMIP5) simulations. In this aim, an energy-balance model (EBM), with one box representing the land area and two other boxes the near-surface and the deep ocean, is developed. In particular, a simple parameterization of the horizontal energy transport (HET) change between these two regions is proposed. The EBM is shown to capture the variation of the land and the ocean temperature responses and of the land-sea warming ratio in different idealized climate change experiments. By using this framework, we first show that the land-sea warming contrast is explained by the asymmetry in the strength of the HET between the land and ocean and not by land-sea differences in radiative feedbacks. Then we use a method of analysis of variance to infer the contributors to the intermodel spread in the land-sea warming ratio of climate models participating to CMIP5. The main contributor is found to be the HET with a contribution of about 70 %. Finally, our results suggest that the asymmetric character of the HET dependency to the land and the ocean temperature responses may be primarily explained by the land-sea differences in surface specific humidity change for a given temperature change.

Published
2015

12. Transient Climate Response in a Two-Layer Energy-Balance Model. Part II: Representation of the Efficacy of Deep-Ocean Heat Uptake and Validation for CMIP5 AOGCMs

Author

D. Olivié, Gilles Bellon, Olivier Geoffroy, Aurore Voldoire, S. Tyteca, and David Saint-Martin

Subjects
Atmospheric Science, Coupled model intercomparison project, 010504 meteorology & atmospheric sciences, Energy balance, Radiative forcing, 010502 geochemistry & geophysics, 01 natural sciences, 13. Climate action, Climatology, Radiative transfer, Climate sensitivity, Environmental science, Climate model, Transient response, Transient (oscillation), 0105 earth and related environmental sciences
Abstract

In this second part of a series of two articles analyzing the global thermal properties of atmosphere–ocean coupled general circulation models (AOGCMs) within the framework of a two-layer energy-balance model (EBM), the role of the efficacy of deep-ocean heat uptake is investigated. Taking into account such an efficacy factor is shown to amount to representing the effect of deep-ocean heat uptake on the local strength of the radiative feedback in the transient regime. It involves an additional term in the formulation of the radiative imbalance at the top of the atmosphere (TOA), which explains the nonlinearity between radiative imbalance and the mean surface temperature observed in some AOGCMs. An analytical solution of this system is given and this simple linear EBM is calibrated for the set of 16 AOGCMs of phase 5 of the Coupled Model Intercomparison Project (CMIP5) studied in Part I. It is shown that both the net radiative fluxes at TOA and the global surface temperature transient response are well represented by the simple EBM over the available period of simulations. Differences between this two-layer EBM and the previous version without an efficacy factor are analyzed and relationships between parameters are discussed. The simple model calibration applied to AOGCMs constitutes a new method for estimating their respective equilibrium climate sensitivity and adjusted radiative forcing amplitude from short-term step-forcing simulations and more generally a method to compute their global thermal properties.

Published
2013

13. Adjusted radiative forcing and global radiative feedbacks in CNRM-CM5, a closure of the partial decomposition

Author

David Salas y Mélia, Aurore Voldoire, Olivier Geoffroy, Stephane Sénési, and David Saint-Martin

Subjects
Atmospheric Science, 010504 meteorology & atmospheric sciences, Perturbation (astronomy), Radiative forcing, 010502 geochemistry & geophysics, 01 natural sciences, Cloud feedback, Radiative flux, 13. Climate action, Climatology, Linear regression, Radiative transfer, Climate sensitivity, Environmental science, Climate model, 0105 earth and related environmental sciences
Abstract

This study provides a comprehensive global analysis of the climate radiative feedbacks and the adjusted radiative forcing for a CO2 increase perturbation in the CNRM-CM5 climate model using the partial radiative perturbations (PRP) method. Some methodological key points of the PRP are investigated, with a particular focus on the consideration of the effect of fast adjustments. First, the standard PRP method is applied by neglecting certain fast adjustments. The effect of the field decorrelation is highlighted by performing a PRP across two different periods of a control experiment and by analyzing second-order terms. Sensitivity tests to the field substitution frequency, the sampling period and the perturbed experiment used are performed. The impact of the definition of the top of the climate system (top-of-the-atmosphere or tropopause) in the feedback estimate is also discussed. Secondly, the fast adjustment processes are taken into account by combining the PRP framework with the method of linear regression of the partial net radiative flux change against the mean surface air temperature change using a step forcing experiment. This method allows us to quantify the contribution of the different constituents to the forcing adjustment and to improve the estimation of the radiative feedbacks. It is shown that such decomposition allows the retrieval of the adjusted radiative forcing, the radiative feedbacks and the climate sensitivity as estimated with the linear regression method with a high level of accuracy, validating the partial decomposition.

Published
2013
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14. Transient Climate Response in a Two-Layer Energy-Balance Model. Part I: Analytical Solution and Parameter Calibration Using CMIP5 AOGCM Experiments

Author

D. Olivié, Gilles Bellon, S. Tyteca, Olivier Geoffroy, Aurore Voldoire, and David Saint-Martin

Subjects
Atmospheric Science, Forcing (recursion theory), 010504 meteorology & atmospheric sciences, 0207 environmental engineering, Energy balance, 02 engineering and technology, Radiative forcing, 01 natural sciences, 13. Climate action, Climatology, Thermal, Radiative transfer, Climate sensitivity, Climate model, Transient (oscillation), 020701 environmental engineering, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences, Mathematics
Abstract

This is the first part of a series of two articles analyzing the global thermal properties of atmosphere–ocean coupled general circulation models (AOGCMs) within the framework of a two-layer energy-balance model (EBM). In this part, the general analytical solution of the system is given and two idealized climate change scenarios, one with a step forcing and one with a linear forcing, are discussed. These solutions give a didactic description of the contributions from the equilibrium response and of the fast and slow transient responses during a climate transition. Based on these analytical solutions, a simple and physically based procedure to calibrate the two-layer model parameters using an AOGCM step-forcing experiment is introduced. Using this procedure, the global thermal properties of 16 AOGCMs participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) are determined. It is shown that, for a given AOGCM, the EBM tuned with only the abrupt 4×CO2 experiment is able to reproduce with a very good accuracy the temperature evolution in both a step-forcing and a linear-forcing experiment. The role of the upper-ocean and deep-ocean heat uptakes in the fast and slow responses is also discussed. One of the main weaknesses of the simple EBM discussed in this part is its ability to represent the evolution of the top-of-the-atmosphere radiative imbalance in the transient regime. This issue is addressed in Part II by taking into account the efficacy factor of deep-ocean heat uptake.

Published
2013
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15. The respective roles of surface temperature driven feedbacks and tropospheric adjustment to CO2 in CMIP5 transient climate simulations

Author

Jean-Louis Dufresne, Thorsten Mauritsen, Olivier Geoffroy, Abderrahmane Idelkadi, Lorenzo Tomassini, Johannes Quaas, Marco Giorgetta, Karoline Block, Chiara Cagnazzo, Courant Research Centre 'Higher Order Structures' (CRC), Laboratoire de Génie Electrique de Grenoble (G2ELab), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut Polytechnique de Grenoble - Grenoble Institute of Technology-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Istituto di Scienze dell'Atmosfera e del Clima (ISAC), National Research Council of Italy | Consiglio Nazionale delle Ricerche (CNR), Max Planck Institute for Meteorology (MPI-M), Max-Planck-Gesellschaft, Max-Planck-Institut für Meteorologie (MPI-M), Universität Leipzig, Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École des Ponts ParisTech (ENPC)-École polytechnique (X)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Consiglio Nazionale delle Ricerche [Roma] (CNR), and Universität Leipzig [Leipzig]

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Atmospheric Science, 010504 meteorology & atmospheric sciences, Cloud fraction, Longwave, Climate change, 010502 geochemistry & geophysics, Atmospheric sciences, 01 natural sciences, Cloud feedback, Troposphere, 13. Climate action, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, Climatology, Environmental science, Climate model, Tropopause, Shortwave, 0105 earth and related environmental sciences
Abstract

International audience; An overview of radiative climate feedbacks and ocean heat uptake efficiency diagnosed from idealized transient climate change experiments of 14 CMIP5 models is presented. Feedbacks explain about two times more variance in transient climate response across the models than ocean heat uptake efficiency. Cloud feedbacks can clearly be identified as the main source of inter-model spread. Models with strong longwave feedbacks in the tropics feature substantial increases in cloud ice around the tropopause suggestive of changes in cloud-top heights. The lifting of the tropical tropopause goes together with a general weakening of the tropical circulation. Distinctive inter-model differences in cloud shortwave feedbacks occur in the subtropics including the equatorward flanks of the storm-tracks. Related cloud fraction changes are not confined to low clouds but comprise middle level clouds as well. A reduction in relative humidity through the lower and mid troposphere can be identified as being the main associated large-scale feature. Experiments with prescribed sea surface temperatures are analyzed in order to investigate whether the diagnosed feedbacks from the transient climate simulations contain a tropospheric adjustment component that is not conveyed through the surface temperature response. The strengths of the climate feedbacks computed from atmosphere-only experiments with prescribed increases in sea surface temperatures, but fixed CO2 concentrations, are close to the ones derived from the transient experiment. Only the cloud shortwave feedback exhibits discernible differences which, however, can not unequivocally be attributed to tropospheric adjustment to CO2. Although for some models a tropospheric adjustment component is present in the global mean shortwave cloud feedback, an analysis of spatial patterns does not lend support to the view that cloud feedbacks are dominated by their tropospheric adjustment part. Nevertheless, there is positive correlation between the strength of tropospheric adjustment processes and cloud feedbacks across different climate models.

Published
2013

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