Hervé Le Treut worked as IPSL Director for IPCC between 2008 and 2019. He built his internationally recognized research career at Polytechnique, Sorbonne University and ENS, France. He co-created AcclimaTerra and received several distinctions. He is a knight of the Legion of Honor.Mounia Mostefaoui graduated from Polytechnique and completed her PhD in physics of climate change at LMD-IPSL, France. Her advisors were Hervé Le Treut and Philippe Ciais. She was Expert Reviewer for the AR6 IPCC report and participated in several COPs as a speaker in the IPCC Pavilion.

• Preface ixChapter 1 A Description of the Main Constraints Regulating the Earth Climate 11.1 Generalities about the atmosphere and the ocean 11.1.1 The atmosphere 41.1.2 A brief comparison between some oceans and the atmosphere’s main orders of magnitude 91.2 A global view of radiative processes 91.3 Past climate history 181.4 A global evaluation of climate stability 321.4.1 Let us consider the first term of equation [1.8] 331.4.2 Let us consider the second term of equation [1.8] 371.4.3 A global estimate of climate stability considering another source of complexity: the greenhouse effect 431.5 Conclusion 47Chapter 2 The Vertical Dimension of the Energy Processes of the Climate System: Radiative Processes and Radiative–Convective Models 492.1 Radiative processes: generalities 502.2 Absorption and greenhouse effect 522.3 The role of convection 622.3.1 Where does the - F ± comes from? 642.4 Diffusion of solar radiation 78Chapter 3 The Horizontal Motion of Atmospheric and Oceanic Transport 933.1 Energy budget at the top of the atmosphere 933.2 Energy exchanges with the surface 983.3 Transport by the atmosphere and the ocean 1133.4 Vertical and horizontal transports: the links 1173.4.1 What is stable stratification? 1243.5 Conclusion 141Chapter 4 A Transition from Quasi-Equilibrium to Forcing from Anthropogenic Source: A Cartography of Predictable Phenomena, Uncertainties and Feedback Related to the Climate Response to Anthropogenic Disturbance 1434.1 A transitory evolution 1444.1.1 Presentation of the Intergovernmental Panel on Climate Change (IPCC) and its missions 1474.1.2 A focus on IPCC productions 1484.1.3 Examples of IPCC production impacts 1504.1.4 Complexity, a main feature of the Earth climate system transitory evolution 1514.2 Global temperature change and the role of feedbacks 1784.2.1. About models’ uncertainties and radiative forcing associated with CO 2 1854.2.2 The water vapor feedback 1884.2.3 The albedo feedback 1894.2.4 The cloud feedback 1904.2.5 The lapse-rate feedback 1924.3 Measured and anticipated impacts: what is predictable? 1974.3.1 Three generations of model assessments directed toward climate change 1984.3.2 Socio-economic pathways (SSP) in AR6 2054.3.3. Articulation between SSP scenarios from AR 6 and RCP scenarios from AR5 2074.3.4 As for the most probable trajectory currently followed 2104.3.5 Main novelties for the seventh IPCC Assessment Report 2134.3.6 Method for the evaluation of a probability in IPCC reports 214Chapter 5 From Scientific Diagnostic to Decision-Making 2355.1 The role of uncertainties on assessing global warming, accounting for natural variability and estimating climate impacts 2365.1.1 Process studies and uncertainties 2605.1.2 From natural variability to climate impacts 2795.1.3 Zoom about uncertainties and the IPCC 2815.1.4 Process of uncertainty evaluations by the IPCC as detailed in the Fifth Assessment Report (AR5) 2835.1.5 Process of uncertainty evaluations by the IPCC as detailed in the Sixth Assessment Report (AR6) 2875.1.6 Method for the evaluation of a probability in IPCC reports 2895.2 From global to local climate features: a key shift for the interaction between science and decision-making 2905.3 From scientific diagnosis to political decision-making 3005.4 A word of conclusion 301Appendix 303References 327List of Authors 339Index 341

Hervé Le Treut worked as IPSL Director for IPCC between 2008 and 2019. He built his internationally recognized research career at Polytechnique, Sorbonne University and ENS, France. He co-created AcclimaTerra and received several distinctions. He is a knight of the Legion of Honor.Mounia Mostefaoui graduated from Polytechnique and completed her PhD in physics of climate change at LMD-IPSL, France. Her advisors were Hervé Le Treut and Philippe Ciais. She was Expert Reviewer for the AR6 IPCC report and participated in several COPs as a speaker in the IPCC Pavilion.

• Preface ixChapter 1 A Description of the Main Constraints Regulating the Earth Climate 11.1 Generalities about the atmosphere and the ocean 11.1.1 The atmosphere 41.1.2 A brief comparison between some oceans and the atmosphere’s main orders of magnitude 91.2 A global view of radiative processes 91.3 Past climate history 181.4 A global evaluation of climate stability 321.4.1 Let us consider the first term of equation [1.8] 331.4.2 Let us consider the second term of equation [1.8] 371.4.3 A global estimate of climate stability considering another source of complexity: the greenhouse effect 431.5 Conclusion 47Chapter 2 The Vertical Dimension of the Energy Processes of the Climate System: Radiative Processes and Radiative–Convective Models 492.1 Radiative processes: generalities 502.2 Absorption and greenhouse effect 522.3 The role of convection 622.3.1 Where does the - F ± comes from? 642.4 Diffusion of solar radiation 78Chapter 3 The Horizontal Motion of Atmospheric and Oceanic Transport 933.1 Energy budget at the top of the atmosphere 933.2 Energy exchanges with the surface 983.3 Transport by the atmosphere and the ocean 1133.4 Vertical and horizontal transports: the links 1173.4.1 What is stable stratification? 1243.5 Conclusion 141Chapter 4 A Transition from Quasi-Equilibrium to Forcing from Anthropogenic Source: A Cartography of Predictable Phenomena, Uncertainties and Feedback Related to the Climate Response to Anthropogenic Disturbance 1434.1 A transitory evolution 1444.1.1 Presentation of the Intergovernmental Panel on Climate Change (IPCC) and its missions 1474.1.2 A focus on IPCC productions 1484.1.3 Examples of IPCC production impacts 1504.1.4 Complexity, a main feature of the Earth climate system transitory evolution 1514.2 Global temperature change and the role of feedbacks 1784.2.1. About models’ uncertainties and radiative forcing associated with CO 2 1854.2.2 The water vapor feedback 1884.2.3 The albedo feedback 1894.2.4 The cloud feedback 1904.2.5 The lapse-rate feedback 1924.3 Measured and anticipated impacts: what is predictable? 1974.3.1 Three generations of model assessments directed toward climate change 1984.3.2 Socio-economic pathways (SSP) in AR6 2054.3.3. Articulation between SSP scenarios from AR 6 and RCP scenarios from AR5 2074.3.4 As for the most probable trajectory currently followed 2104.3.5 Main novelties for the seventh IPCC Assessment Report 2134.3.6 Method for the evaluation of a probability in IPCC reports 214Chapter 5 From Scientific Diagnostic to Decision-Making 2355.1 The role of uncertainties on assessing global warming, accounting for natural variability and estimating climate impacts 2365.1.1 Process studies and uncertainties 2605.1.2 From natural variability to climate impacts 2795.1.3 Zoom about uncertainties and the IPCC 2815.1.4 Process of uncertainty evaluations by the IPCC as detailed in the Fifth Assessment Report (AR5) 2835.1.5 Process of uncertainty evaluations by the IPCC as detailed in the Sixth Assessment Report (AR6) 2875.1.6 Method for the evaluation of a probability in IPCC reports 2895.2 From global to local climate features: a key shift for the interaction between science and decision-making 2905.3 From scientific diagnosis to political decision-making 3005.4 A word of conclusion 301Appendix 303References 327List of Authors 339Index 341

Hervé Le Treut worked as IPSL Director for IPCC between 2008 and 2019. He built his internationally recognized research career at Polytechnique, Sorbonne University and ENS, France. He co-created AcclimaTerra and received several distinctions. He is a knight of the Legion of Honor.Mounia Mostefaoui graduated from Polytechnique and completed her PhD in physics of climate change at LMD-IPSL, France. Her advisors were Hervé Le Treut and Philippe Ciais. She was Expert Reviewer for the AR6 IPCC report and participated in several COPs as a speaker in the IPCC Pavilion.

• Preface ixChapter 1 A Description of the Main Constraints Regulating the Earth Climate 11.1 Generalities about the atmosphere and the ocean 11.1.1 The atmosphere 41.1.2 A brief comparison between some oceans and the atmosphere’s main orders of magnitude 91.2 A global view of radiative processes 91.3 Past climate history 181.4 A global evaluation of climate stability 321.4.1 Let us consider the first term of equation [1.8] 331.4.2 Let us consider the second term of equation [1.8] 371.4.3 A global estimate of climate stability considering another source of complexity: the greenhouse effect 431.5 Conclusion 47Chapter 2 The Vertical Dimension of the Energy Processes of the Climate System: Radiative Processes and Radiative–Convective Models 492.1 Radiative processes: generalities 502.2 Absorption and greenhouse effect 522.3 The role of convection 622.3.1 Where does the - F ± comes from? 642.4 Diffusion of solar radiation 78Chapter 3 The Horizontal Motion of Atmospheric and Oceanic Transport 933.1 Energy budget at the top of the atmosphere 933.2 Energy exchanges with the surface 983.3 Transport by the atmosphere and the ocean 1133.4 Vertical and horizontal transports: the links 1173.4.1 What is stable stratification? 1243.5 Conclusion 141Chapter 4 A Transition from Quasi-Equilibrium to Forcing from Anthropogenic Source: A Cartography of Predictable Phenomena, Uncertainties and Feedback Related to the Climate Response to Anthropogenic Disturbance 1434.1 A transitory evolution 1444.1.1 Presentation of the Intergovernmental Panel on Climate Change (IPCC) and its missions 1474.1.2 A focus on IPCC productions 1484.1.3 Examples of IPCC production impacts 1504.1.4 Complexity, a main feature of the Earth climate system transitory evolution 1514.2 Global temperature change and the role of feedbacks 1784.2.1. About models’ uncertainties and radiative forcing associated with CO 2 1854.2.2 The water vapor feedback 1884.2.3 The albedo feedback 1894.2.4 The cloud feedback 1904.2.5 The lapse-rate feedback 1924.3 Measured and anticipated impacts: what is predictable? 1974.3.1 Three generations of model assessments directed toward climate change 1984.3.2 Socio-economic pathways (SSP) in AR6 2054.3.3. Articulation between SSP scenarios from AR 6 and RCP scenarios from AR5 2074.3.4 As for the most probable trajectory currently followed 2104.3.5 Main novelties for the seventh IPCC Assessment Report 2134.3.6 Method for the evaluation of a probability in IPCC reports 214Chapter 5 From Scientific Diagnostic to Decision-Making 2355.1 The role of uncertainties on assessing global warming, accounting for natural variability and estimating climate impacts 2365.1.1 Process studies and uncertainties 2605.1.2 From natural variability to climate impacts 2795.1.3 Zoom about uncertainties and the IPCC 2815.1.4 Process of uncertainty evaluations by the IPCC as detailed in the Fifth Assessment Report (AR5) 2835.1.5 Process of uncertainty evaluations by the IPCC as detailed in the Sixth Assessment Report (AR6) 2875.1.6 Method for the evaluation of a probability in IPCC reports 2895.2 From global to local climate features: a key shift for the interaction between science and decision-making 2905.3 From scientific diagnosis to political decision-making 3005.4 A word of conclusion 301Appendix 303References 327List of Authors 339Index 341