CCSP 1.3 April 2, 2008 1 2 3 U.S. Climate Change Science Program 4 5 6 Synthesis and Assessment Product 1.3 7 8 Reanalysis of Historical Climate 9 Data for Key Atmospheric Features: 10 Implications for Attribution of 11 Causes of Observed Change 12 13 14 15 Lead Agency: 16 National Oceanic and Atmospheric Administration 17 18 Contributing Agencies: 19 Department of Energy 20 National Aeronautics and Space Administration 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 Note to Reviewers: This report has not yet undergone rigorous copy-editing 36 and will do so prior to layout for publication Do Not Cite or Quote 1 of 332 Public Review Draft CCSP 1.3 April 2, 2008 1 Table of Contents 2 3 ABSTRACT .................................................................................................................................................. 5 4 PREFACE..................................................................................................................................................... 7 5 P.1 OVERVIEW OF REPORT............................................................................................................... 7 6 P.2 PRIMARY REPORT FOCI.............................................................................................................. 9 7 P.2.1 Reanalysis of Historical Climate Data for Key Atmospheric Features................................... 10 8 P.2.2 Attribution of the Causes of Climate Variations and Trends Over North America ............... 11 9 P.3 TREATMENT OF UNCERTAINTY............................................................................................. 13 10 P.4 SCOPE AND LIMITATIONS OF THIS REPORT ...................................................................... 13 11 EXECUTIVE SUMMARY ........................................................................................................................ 17 12 ES.1 PRIMARY RESULTS AND FINDINGS.................................................................................... 19 13 ES.1.1 Strengths and Limitations of Current Reanalysis Data Sets for Representing Key 14 Atmospheric Features (From Chapter 2).......................................................................................... 19 15 ES.1.2 Attribution of the Causes of Climate Variations and Trends Over North America During 16 the Modern Reanalysis Period (From Chapter 3)............................................................................. 22 17 ES.2 RECOMMENDATIONS.............................................................................................................. 24 18 CHAPTER 1. FUNDAMENTAL CONCEPTS........................................................................................ 27 19 FUNDAMENTAL CONCEPTS ........................................................................................................... 27 20 1.1 REANALYSIS.................................................................................................................................. 27 21 1.2 ATTRIBUTION ............................................................................................................................... 32 22 1.3 CONNECTIONS BETWEEN REANALYSIS AND ATTRIBUTION ........................................ 34 23 1.3.1 Medical Diagnosis..................................................................................................................... 35 24 1.3.2 Relationships in Climate Science ............................................................................................. 37 25 1.4 REANALYSIS APPLICATIONS AND USES............................................................................... 40 26 CHAPTER 1 REFERENCES ............................................................................................................... 42 27 CHAPTER 2. RE-ANALYSIS OF HISTORICAL CLIMATE DATA FOR KEY ATMOSPHERIC 28 FEATURES................................................................................................................................................. 46 29 KEY FINDINGS .................................................................................................................................... 46 30 2.1. WHAT IS A CLIMATE REANALYSIS, AND WHAT ROLE DOES REANALYSIS PLAY 31 WITHIN A COMPREHENSIVE CLIMATE OBSERVING SYSTEM?......................................... 49 32 2.1.1 Introduction............................................................................................................................... 49 33 2.1.2 What is a Climate Analysis? ..................................................................................................... 50 34 2.1.3 What is a Climate Reanalysis?.................................................................................................. 58 35 2.1.4. What Role Does Reanalysis Play within a Climate Observing System?................................. 59 36 2.2. WHAT CAN REANALYSIS TELL US ABOUT CLIMATE FORCING AND THE 37 VERACITY OF CLIMATE MODELS? ............................................................................................. 66 38 2.2.1 Introduction............................................................................................................................... 66 39 2.2.2 Assessing Systematic Errors ..................................................................................................... 67 40 2.2.3 Inferences about Climate Forcing............................................................................................ 70 41 2.2.4 Outlook ...................................................................................................................................... 73 42 2.3. WHAT IS THE CAPACITY OF CURRENT REANALYSES TO HELP US IDENTIFY AND 43 UNDERSTAND MAJOR SEASONAL-TO-DECADAL CLIMATE VARIATIONS, INCLUDING 44 CHANGES IN THE FREQUENCY AND INTENSITY OF CLIMATE EXTREMES SUCH AS 45 DROUGHTS? ........................................................................................................................................ 74 46 2.3.1. Climate Variability ................................................................................................................... 75 47 2.3.2 Reanalysis and Climate Variability .......................................................................................... 81 48 2.4 TO WHAT EXTENT IS THERE AGREEMENT OR DISAGREEMENT BETWEEN 49 CLIMATE TRENDS IN SURFACE TEMPERATURE AND PRECIPITATION DERIVED 50 FROM REANALYSES AND THOSE DERIVED FROM INDEPENDENT DATA? .................... 97 51 2.4.1. Trend Comparisons: Reanalyses Versus Independent Measurements .................................. 99 Do Not Cite or Quote 2 of 332 Public Review Draft CCSP 1.3 April 2, 2008 1 2.4.2. Factors Complicating the Calculation of Trends.................................................................. 104 2 2.4.3. Outlook ................................................................................................................................... 110 3 2.5 WHAT STEPS WOULD BE MOST USEFUL IN REDUCING SPURIOUS TRENDS AND 4 OTHER MAJOR UNCERTAINTIES IN DESCRIBING THE PAST BEHAVIOR OF THE 5 CLIMATE SYSTEM THROUGH REANALYSIS METHODS? SPECIFICALLY, WHAT 6 CONTRIBUTIONS COULD BE MADE THROUGH IMPROVEMENTS IN DATA RECOVERY 7 OR QUALITY CONTROL, MODELING, OR DATA ASSIMILATION TECHNIQUES?........ 113 8 2.5.1 Instrument and Sampling Issues....................................................................................... 113 9 2.5.2 Modeling and Data Assimilation Issues................................................................................. 122 10 CHAPTER 2 REFERENCES ............................................................................................................. 129 11 APPENDIX 2.A DATA ASSIMILATION.................................................................................................... 152 12 CHAPTER 3. ATTRIBUTION OF THE CAUSES OF CLIMATE VARIATIONS AND TRENDS 13 OVER NORTH AMERICA DURING THE MODERN REANALYSIS PERIOD............................ 156 14 KEY FINDINGS .................................................................................................................................. 156 15 INTRODUCTION ............................................................................................................................... 159 16 3.1 WHAT IS CLIMATE ATTRIBUTION, AND WHAT ARE THE SCIENTIFIC METHODS 17 USED FOR ESTABLISHING ATTRIBUTION?.............................................................................. 165 18 3.1.1 What is Attribution?................................................................................................................ 165 19 3.1.2 How is Attribution Performed?............................................................................................... 167 20 3.2 WHAT IS THE PRESENT UNDERSTANDING OF THE CAUSES FOR THE NORTH 21 AMERICAN CLIMATE TRENDS IN ANNUAL TEMPERATURE AND PRECIPITATION 22 DURING THE REANALYSIS PERIOD? ......................................................................................... 185 23 3.2.1 Summary of IPCC Fourth Assessment Report ...................................................................... 185 24 3.2.2 North American Annual Mean Temperature......................................................................... 188 25 3.3 WHAT IS THE PRESENT UNDERSTANDING OF THE CAUSES FOR THE SEASONAL 26 AND REGIONAL DIFFERENCES IN UNITED STATES TEMPERATURE AND 27 PRECIPITATION TRENDS DURING THE REANALYSIS PERIOD?........................................ 205 28 3.3.1 Introduction............................................................................................................................