First Order Draft Chapter 9 IPCC WGI Fifth Assessment Report 1 2 Chapter 9: Evaluation of Climate Models 3 4 Coordinating Lead Authors: Gregory Flato (Canada), Jochem Marotzke (Germany) 5 6 Lead Authors: Babatunde Abiodun (South Africa), Pascale Braconnot (France), Sin Chan Chou (Brazil), 7 William Collins (USA), Peter Cox (UK), Fatima Driouech (Morocco), Seita Emori (Japan), Veronika Eyring 8 (Germany), Chris Forest (USA), Peter Gleckler (USA), Eric Guilyardi (France), Christian Jakob (Australia), 9 Vladimir Kattsov (Russia), Chris Reason (South Africa), Markku Rummukainen (Sweden) 10 11 Contributing Authors: Alessandro Anav, Timothy Andrews, Johanna Baehr, Alejandro Bodas-Salcedo, 12 Ping Chang, Aiguo Dai, Clara Deser, Bode Gbobaniyi, Fidel Gonzales-Rouco, Stephen Griffies, Alex Hall, 13 Elizabeth Hunke, Tatiana Ilyina, Viatcheslav Kharin, Stephen A. Klein, Jeff Knight, Reto Knutti, Felix 14 Landerer, Tatiana Pavlova, Florian Rauser, Mark Rodwell, Adam A. Scaife, John Scinocca, Hideo 15 Shiogama, Jana Sillmann, Ken Sperber, David Stephenson, Bjorn Stevens, Mark Webb, Keith Williams, Tim 16 Woollings, Shang-Ping Xie 17 18 Review Editors: Isaac Held (USA), Andy Pitman (Australia), Serge Planton (France), Zong-Ci Zhao 19 (China) 20 21 Date of Draft: 16 December 2011 22 23 Notes: TSU Compiled Version 24 25 26 Table of Contents 27 28 Executive Summary ......................................................................................................................................... 3 29 9.1 Climate Models and their Characteristics ............................................................................................ 5 30 9.1.1 Scope and Overview of this Chapter .............................................................................................. 5 31 9.1.2 Overview of Models to be Evaluated ............................................................................................. 5 32 9.1.3 The Path to Model Improvement .................................................................................................... 6 33 Box 9.1: Model Tuning and Evaluation ......................................................................................................... 7 34 9.2 Techniques for Assessing Model Performance ................................................................................... 15 35 9.2.1 Objectives and Limitations .......................................................................................................... 15 36 9.2.2 New Developments in Model Evaluation Approaches ................................................................. 16 37 9.2.3 Overall Summary of Approach that will be Taken in this Chapter .............................................. 19 38 9.3 Experimental Strategies in Support of Climate Model Evaluation .................................................. 20 39 9.3.1 The Role of Model Intercomparisons ........................................................................................... 20 40 9.3.2 Experimental Strategy for CMIP5 ............................................................................................... 20 41 9.4 Simulation of Recent and Longer-Term Records in Global Models ................................................ 21 42 9.4.1 Atmosphere .................................................................................................................................. 21 43 9.4.2 Ocean ........................................................................................................................................... 30 44 9.4.3 Sea Ice .......................................................................................................................................... 35 45 9.4.4 Land Surface, Fluxes, and Hydrology ......................................................................................... 37 46 9.4.5 Carbon Cycle ............................................................................................................................... 38 47 9.4.6 Sulfur Cycle .................................................................................................................................. 40 48 9.5 Simulation of Variability and Extremes .............................................................................................. 42 49 9.5.1 Importance of Simulating Climate Variability ............................................................................. 42 50 9.5.2 Diurnal-to-Seasonal Variability .................................................................................................. 42 51 9.5.3 Interannual-to-Centennial Variability ......................................................................................... 45 52 9.5.4 Extreme Events............................................................................................................................. 53 53 9.6 Downscaling and Simulation of Regional-Scale Climate ................................................................... 54 54 9.6.1 Regional-Scale Simulation by AOGCMs ..................................................................................... 55 55 9.6.2 Regional Climate Downscaling ................................................................................................... 56 56 9.6.3 Fidelity of Downscaling Methods and Value Added .................................................................... 56 57 9.7 Sources of Model Errors and Uncertainty .......................................................................................... 59 Do Not Cite, Quote or Distribute 9-1 Total pages: 171 First Order Draft Chapter 9 IPCC WGI Fifth Assessment Report 1 9.7.1 Approach to Linking Process Understanding and Model Performance ...................................... 59 2 9.7.2 Process Oriented Evaluation ....................................................................................................... 59 3 9.7.3 Targeted Experiments .................................................................................................................. 60 4 9.7.4 Climate Sensitivity and Climate Feedbacks ................................................................................. 64 5 9.8 Relating Model Performance to Credibility of Model Applications ................................................. 68 6 9.8.1 Overall Assessment of Model Performance ................................................................................. 68 7 9.8.2 Implications of Model Evaluation for Climate Change Detection and Attribution ..................... 70 8 9.8.3 Implications of Model Evaluation for Model Applications to Future Climate ............................ 70 9 FAQ 9.1: Are Climate Models Getting Better, and How Would We Know? ........................................... 72 10 References ...................................................................................................................................................... 74 11 Tables ............................................................................................................................................................ 110 12 Figures .......................................................................................................................................................... 125 13 14 Do Not Cite, Quote or Distribute 9-2 Total pages: 171 First Order Draft Chapter 9 IPCC WGI Fifth Assessment Report 1 Executive Summary 2 3 Climate models play an important role in climate research, enhancing our ability to understand past climate 4 change and providing quantitative information about the future. Confidence in using climate models is based 5 on careful evaluation of model performance, making use of increasingly comprehensive observationally- 6 based data sets and well-designed model intercomparison activities. This chapter provides an assessment of 7 climate model evaluation, focusing particularly on developments since the IPCC Fourth Assessment Report 8 (AR4). A range of models are considered, including: 9 10 • coupled Atmosphere-Ocean General Circulation Models (AOGCMs), used in both long-term climate 11 projection and shorter-term (seasonal to decadal) climate prediction; 12 13 • their extension to ‘Earth System’ Models (ESMs), in which representation of climatically important 14 biogeochemical cycles are included; 15 16 • higher resolution, limited-area Regional Climate Models (RCMs), used extensively in downscaling global 17 climate results to particular regions; 18 19 • Earth System Models of Intermediate Complexity (EMICs) used to undertake very long (e.g., millennial) 20 climate simulations, or to provide large ensembles exploring parameter uncertainty. 21 22 The evaluation of climate models depends directly on the availability of high-quality observational data sets 23 whose uncertainty is understood and quantified. These observational data have been described in earlier 24 chapters. A particular advance since the AR4 has been in the area of model ‘metrics’ – that is, numerical 25 measures of model performance reflecting the difference between a model and a corresponding observational 26 estimate. These metrics allow more systematic evaluation of models and more concise presentation of 27 evaluation results. This chapter will make extensive use of such metrics, along with more traditional 28 presentation of ‘error maps’ and time series. 29 30 Another advance since the AR4 is the extensive use of ‘satellite simulators’ in climate models. This involves 31 on-line calculations which provide