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This chapter should be cited as:
Flato, G., J. Marotzke, B. Abiodun, P. Braconnot, S.C. Chou, W. Collins, P. Cox, F. Driouech, S. Emori, V. Eyring, C.
Forest, P. Gleckler, E. Guilyardi, C. Jakob, V. Kattsov, C. Reason and M. Rummukainen, 2013: Evaluation of Climate
Models. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assess-
ment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor,
S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge,
United Kingdom and New York, NY, USA.
Coordinating Lead Authors:
Gregory Flato (Canada), Jochem Marotzke (Germany)
Lead Authors:
Babatunde Abiodun (South Africa), Pascale Braconnot (France), Sin Chan Chou (Brazil), William
Collins (USA), Peter Cox (UK), Fatima Driouech (Morocco), Seita Emori (Japan), Veronika
Eyring (Germany), Chris Forest (USA), Peter Gleckler (USA), Eric Guilyardi (France), Christian
Jakob (Australia), Vladimir Kattsov (Russian Federation), Chris Reason (South Africa), Markku
Rummukainen (Sweden)
Contributing Authors:
Krishna AchutaRao (India), Alessandro Anav (UK), Timothy Andrews (UK), Johanna Baehr
(Germany), Nathaniel L. Bindoff (Australia), Alejandro Bodas-Salcedo (UK), Jennifer Catto
(Australia), Don Chambers (USA), Ping Chang (USA), Aiguo Dai (USA), Clara Deser (USA),
Francisco Doblas-Reyes (Spain), Paul J. Durack (USA/Australia), Michael Eby (Canada), Ramon
de Elia (Canada), Thierry Fichefet (Belgium), Piers Forster (UK), David Frame (UK/New Zealand),
John Fyfe (Canada), Emiola Gbobaniyi (Sweden/Nigeria), Nathan Gillett (Canada), Jesus Fidel
González-Rouco (Spain), Clare Goodess (UK), Stephen Griffies (USA), Alex Hall (USA), Sandy
Harrison (Australia), Andreas Hense (Germany), Elizabeth Hunke (USA), Tatiana Ilyina (Germany),
Detelina Ivanova (USA), Gregory Johnson (USA), Masa Kageyama (France), Viatcheslav Kharin
(Canada), Stephen A. Klein (USA), Jeff Knight (UK), Reto Knutti (Switzerland), Felix Landerer
(USA), Tong Lee (USA), Hongmei Li (Germany/China), Natalie Mahowald (USA), Carl Mears
(USA), Gerald Meehl (USA), Colin Morice (UK), Rym Msadek (USA), Gunnar Myhre (Norway),
J. David Neelin (USA), Jeff Painter (USA), Tatiana Pavlova (Russian Federation), Judith Perlwitz
(USA), Jean-Yves Peterschmitt (France), Jouni Räisänen (Finland), Florian Rauser (Germany),
Jeffrey Reid (USA), Mark Rodwell (UK), Benjamin Santer (USA), Adam A. Scaife (UK), Jörg
Schulz (Germany), John Scinocca (Canada), David Sexton (UK), Drew Shindell (USA), Hideo
Shiogama (Japan), Jana Sillmann (Canada), Adrian Simmons (UK), Kenneth Sperber (USA),
David Stephenson (UK), Bjorn Stevens (Germany), Peter Stott (UK), Rowan Sutton (UK), Peter
W. Thorne (USA/Norway/UK), Geert Jan van Oldenborgh (Netherlands), Gabriel Vecchi (USA),
Mark Webb (UK), Keith Williams (UK), Tim Woollings (UK), Shang-Ping Xie (USA), Jianglong
Zhang (USA)
Review Editors:
Isaac Held (USA), Andy Pitman (Australia), Serge Planton (France), Zong-Ci Zhao (China)
Evaluation of
Climate Models
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9
Table of Contents
Executive Summary ..................................................................... 743
9.1 Climate Models and Their Characteristics ............... 746
9.1.1 Scope and Overview of this Chapter ......................... 746
9.1.2 Overview of Model Types to Be Evaluated ................ 746
9.1.3 Model Improvements ................................................ 748
Box 9.1: Climate Model Development and Tuning ................ 749
9.2 Techniques for Assessing Model Performance ....... 753
9.2.1 New Developments in Model Evaluation
Approaches ............................................................... 753
9.2.2 Ensemble Approaches for Model Evaluation ............. 754
9.2.3 The Model Evaluation Approach Used in this
Chapter and Its Limitations ....................................... 755
9.3 Experimental Strategies in Support of Climate
Model Evaluation ............................................................ 759
9.3.1 The Role of Model Intercomparisons ......................... 759
9.3.2 Experimental Strategy for Coupled Model
Intercomparison Project Phase 5 ............................... 759
9.4 Simulation of Recent and Longer-Term Records
in Global Models ............................................................. 760
9.4.1 Atmosphere .............................................................. 760
Box 9.2: Climate Models and the Hiatus in Global Mean
Surface Warming of the Past 15 Years .................................... 769
9.4.2 Ocean ........................................................................ 777
9.4.3 Sea Ice ...................................................................... 787
9.4.4 Land Surface, Fluxes and Hydrology .......................... 790
9.4.5 Carbon Cycle ............................................................. 792
9.4.6 Aerosol Burdens and Effects on Insolation ................ 794
9.5 Simulation of Variability and Extremes .................... 795
9.5.1 Importance of Simulating Climate Variability ............ 795
9.5.2 Diurnal-to-Seasonal Variability .................................. 796
9.5.3 Interannual-to-Centennial Variability ........................ 799
9.5.4 Extreme Events ......................................................... 806
Box 9.3: Understanding Model Performance ......................... 809
9.6 Downscaling and Simulation of Regional-Scale
Climate ............................................................................... 810
9.6.1 Global Models ........................................................... 810
9.6.2 Regional Climate Downscaling ................................. 814
9.6.3 Skill of Downscaling Methods ................................... 814
9.6.4 Value Added through RCMs ...................................... 815
9.6.5 Sources of Model Errors and Uncertainties ............... 815
9.6.6 Relating Downscaling Performance to Credibility
of Regional Climate Information ............................... 816
9.7 Climate Sensitivity and Climate Feedbacks ............ 817
9.7.1 Equilibrium Climate Sensitivity, Idealized Radiative
Forcing, and Transient Climate Response in the
Coupled Model Intercomparison Project
Phase 5 Ensemble ..................................................... 817
9.7.2 Understanding the Range in Model Climate
Sensitivity: Climate Feedbacks .................................. 819
9.7.3 Climate Sensitivity and Model Performance .............. 820
9.8 Relating Model Performance to Credibility of
Model Applications ......................................................... 821
9.8.1 Synthesis Assessment of Model Performance ............ 821
9.8.2 Implications of Model Evaluation for Climate
Change Detection and Attribution ............................ 825
9.8.3 Implications of Model Evaluation for Model
Projections of Future Climate .................................... 825
References .................................................................................. 828
Appendix 9.A: Climate Models Assessed
in Chapter 9 .................................................................................. 854
Frequently Asked Questions
FAQ 9.1 Are Climate Models Getting Better, and How
Would We Know? ................................................... 824
743
Evaluation of Climate Models Chapter 9
9
1
In this Report, the following summary terms are used to describe the available evidence: limited, medium, or robust; and for the degree of agreement: low, medium, or high.
A level of confidence is expressed using five qualifiers: very low, low, medium, high, and very high, and typeset in italics, e.g., medium confidence. For a given evidence and
agreement statement, different confidence levels can be assigned, but increasing levels of evidence and degrees of agreement are correlated with increasing confidence (see
Section 1.4 and Box TS.1 for more details).
Executive Summary
Climate models have continued to be developed and improved
since the AR4, and many models have been extended into Earth
System models by including the representation of biogeochem-
ical cycles important to climate change. These models allow for
policy-relevant calculations such as the carbon dioxide (CO
2
) emissions
compatible with a specified climate stabilization target. In addition, the
ran