IMPACT OF WEATHER AND CLIMATE EXTREMES -- IMPACT OF WEATHER AND CLIMATE EXTREMES -- CONTENTS -- PREFACE -- Chapter 1 WEATHER AND CLIMATE EXTREMES IN A CHANGING CLIMATE (REGIONS OF FOCUS: NORTH AMERICA, HAWAII, CARIBBEAN, AND U.S. PACIFIC ISLANDS)* -- ACKNOWLEDGMENT -- SYNOPSIS -- EXECUTIVE SUMMARY -- Synopsis -- 1. What are Extremes and Why Do They Matter? -- 2. Temperature-Related Extremes -- Observed Changes -- Attribution of Changes -- Projected Changes -- 3. Precipitation Extremes -- Observed Changes -- Attribution of Changes -- Projected Changes -- 4. Drought -- Observed Changes -- Attribution of Changes -- Projected Changes -- 5. Storms -- Hurricanes and Tropical Storms -- Observed changes -- Attribution of Changes -- Projected Changes -- Other Storms -- Observed Changes -- Attribution of Changes -- Projected Changes -- 6. What Measures Can Be Taken to Improve the Understanding of Weather and Climate Extremes? -- 1. WHY WEATHER AND CLIMATE EXTREMES MATTER -- Key Findings -- 1.1. Weather and Climate Extremes Impact People, Plants, and Animals -- 1.2. Extremes are Changing -- 1.3. Nature and Society are Sensitive to Changes in Extremes -- 1.4. Future Impacts of Changing Extremes also Depend on Vulnerability -- 1.5. Systems are Adapted to the Historical Range of Extremes so Changes in Extremes Pose Challenges -- 1.6. Actions Can Increase or Decrease the Impact of Extremes -- 1.7. Assessing Impacts of Changes in Extremes Is Difficult -- 1.8. Summary and Conclusions -- 2. OBSERVED CHANGES IN WEATHER AND CLIMATE EXTREMES -- Key Findings -- Observed Changes -- 2.1. Background -- 2.2. Observed Changes and Variations in Weather and Climate Extremes -- 2.2.1. Temperature Extremes -- 2.2.2. Precipitation Extremes -- 2.2.2.1. Drought -- 2.2.2.2. Short Duration Heavy Precipitation -- 2.2.2.2.1. Data Considerations and Terms.

2.2.2.2.2. United States -- 2.2.2.2.3. Alaska and Canada -- 2.2.2.2.4. Mexico -- 2.2.2.2.5. Summary -- 2.2.2.3. Monthly to Seasonal Heavy Precipitation -- 2.2.2.4. North American Monsoon -- 2.2.2.5. Tropical Storm Rainfall in Western Mexico -- 2.2.2.6. Tropical Storm Rainfall in the Southeastern United States -- 2.2.2.7. Streamflow -- 2.2.3. Storm Extremes -- 2.2.3.1. Tropical Cyclones -- 2.2.3.1.1. Introduction -- 2.2.3.1.2. Data Issues -- 2.2.3.1.3. Low-frequency Variability and Trends of Tropical Cyclone Activity Indices -- 2.2.3.1.4. Low-frequency Variability and Trends of Tropical Cyclone Numbers -- 2.2.3.1.5. Paleoclimate Proxy Studies of Past tropical Cyclone Activity -- 2.2.3.2. Strong Extratropical Cyclones Overview -- 2.2.3.2.1. Variability of Extra-Tropical Cyclone Activity -- 2.2.3.2.2. Changes in Storm Tracks and Extra-Tropical Cyclone Characteristics -- 2.2.3.2.3. Nor'easters -- 2.2.3.3. Coastal Waves: Trends of Increasing Heights and Their Extremes -- 2.2.3.3.1. The Waves of Extratropical Storms and Hurricanes -- 2.2.3.3.2. Atlantic Coast Waves -- 2.2.3.3.3. Pacific Coast Waves -- 2.2.3.4. Winter Storms -- 2.2.3.4.1. Snowstorms -- 2.2.3.4.2. Ice Storms -- 2.2.3.5. Convective Storms -- 2.3. Key Uncertainties Related to Measuring Specific Variations and Change -- 2.3.1. Methods based on Counting Exceedances over a High Threshold -- 2.3.2. The GEV Approach -- 3. CAUSES OF OBSERVED CHANGES IN EXTREMES AND PROJECTIONS OF FUTURE CHANGES -- Key Findings -- Attribution of observed changes -- Projected Changes -- 3.1. Introduction -- 3.2. What are the Physical Mechanisms of Observed Changes in Extremes? -- 3.2.1. Detection and Attribution: Evaluating Human Influences on Climate Extremes over North America -- 3.2.1.1. Detection and Attribution: Human-induced Changes in Average Climate that Affect Climate Extremes.

3.2.1.2. Changes in Modes of Climate-System Behavior Affecting Climate Extremes -- 3.2.2. Changes in Temperature Extremes -- 3.2.3. Changes in Precipitation Extremes -- 3.2.3.1. Heavy Precipitation -- 3.2.3.2. Runoff and Drought -- 3.2.4. Tropical Cyclones -- 3.2.4.1. Criteria and Mechanisms for Tropical Cyclone Development -- 3.2.4.1.1. Factors Influencing Intensity and Duration -- 3.2.4.1.2. Movement Mechanisms -- 3.2.4.2. Attribution Preamble -- 3.2.4.3. Attribution of North Atlantic Changes -- 3.2.4.3.1. Storm Intensity -- 3.2.4.3.2. Storm Frequency and Integrated Activity Measures -- 3.2.4.3.3. Storm Duration, Track, and Extratropical Transition -- 3.2.5. Extratropical Storms -- 3.2.6. Convective Storms -- 3.3. Projected Future Changes in Extremes, their Causes, Mechanisms, and Uncertainties -- 3.3.1. Temperature -- 3.3.2. Frost -- 3.3.3. Growing Season Length -- 3.3.4. Snow Cover and Sea Ice -- 3.3.5. Precipitation -- 3.3.6. Flooding and Dry Days -- 3.3.7. Drought -- 3.3.8. Snowfall -- 3.3.9. Tropical Cyclones (Tropical Storms and Hurricanes) -- 3.3.9.1. Introduction -- 3.3.9.2. Tropical Cyclone Intensity -- 3.3.9.3. Tropical Cyclone Frequency and Area of Genesis -- 3.3.9.4. Tropical Cyclone Precipitation -- 3.3.9.5. Tropical Cyclone Size, Duration, Track, Storm Surge, and Regions of Occurrence -- 3.3.9.6. Reconciliation of Future Projections and Past Variations -- 3.3.10. Extratropical Storms -- 3.3.11. Convective Storms -- 4. MEASURES TO IMPROVE OUR UNDERSTANDING OF WEATHER AND CLIMATE EXTREMES -- Background -- 4.1. The Continued Development and Maintenance of High Quality Climate Observing Systems will Improve Our Ability to Monitor and Detect Future Changes in Climate Extremes.

4.2. Efforts to Digitize, Homogenize, and Analyze Long-Term Observations in the Instrumental Record with Multiple Independent Experts and Analyses Improve Our Confidence in Detecting Past Changes in Climate Extremes -- 4.3. Weather Observing Systems Adhering to Standards of Observation Consistent with the Needs of both the Climate and the Weather Research Communities Improve our Ability to Detect Observed Changes in Climate Extremes -- 4.4. Extended Recontructions of Past Climate Using Weather Models Initialized with Homogenous Surface Observations Would Help Improve Our Understanding of Strong Extratropical Cyclones and other Aspects of Climate Variability -- 4.5. The creation of Annually-Resolved, Regional-Scale Reconstructions of the Climate for the Past 2,000 Years Would Help Improve Our Understanding of Very Long-Term Regional Climate Variability -- 4.6. Improvements in Our Understanding of the Mechanisms that Govern Hurricane Intensity Would Lead to Better Short- and Long-Term Predictive Capabilities -- 4.7. Establishing a Globally-consistent Wind Definition for Determining Hurricane Intensity Would Allow for More Consistent Comparisons across the Globe -- 4.8. Improvements in the Ability of Climate Models to Recreate the Recent Past as Well as Make Projections under a Variety of Forcing Scenarios are Dependent on Access to Both Computational and Human Resources -- 4.9. More Extensive Access to High Temporal Resolution Data (Daily, Hourly) from Climate Model Simulations Both of the Past and for the Future Would Allow for Improved Understanding of Potential Changes in Weather and Climate Extremes -- 4.10. Research Should Focus on the Development of a Better Understanding of the Physical Processes that Produce Extremes and How These Processes Change with Climate.

4.11. Enhanced Communication between the Climate Science Community and Those Who Make Climate-Sensitive Decisions Would Strengthen Our Understanding of Climate Extremes and Their Impacts -- 4.12. A Reliable Database That Links Weather and Climate Extremes with Their Impacts, Including Damages and Costs under Changing Socioeconomic Conditions, Would Help our Understanding of These Events -- 4.13. Summary -- APPENDIX A. STATISTICAL TREND ANALYSIS -- Example 1: Cold Index Data (Section 2.2.1) -- Example 2: Heat Wave Index Data (Section 2.2.1 and Figure 2.3(A)) -- Example 3.1:Day Heavy Precipitation Frequencies (Section 2.1.2.2) -- Example 4: 90-Day Heavy Precipitation Frequencies (Section 2.1.2.3 and Figure 2.9) -- Example 5: Tropical Cyclones in the North Atlantic (Section 2.1.3.1) -- Example 6: U.S. Landfalling Hurricanes (Section 2.1.3.1) -- GLOSSARY AND ACRONYMS -- Glossary -- Acronyms and Abbreviations -- REFERENCES -- End Notes -- Chapter 2 CLIMATE CHANGE: SCIENCE HIGHLIGHTS* -- SUMMARY -- INTRODUCTION -- OBSERVED WARMING AND ADDITIONAL METRICS OF CLIMATE CHANGE -- ATTRIBUTION OF OBSERVED CHANGES MOSTLY TO GREENHOUSE GASES -- Human-Related Influences on Climate Change -- Trends in Atmospheric Concentrations of Greenhouse Gases -- Greenhouse Gas Emissions and Growth Globally -- OBSERVED IMPACTS OF CLIMATE CHANGES -- Extent of Arctic Sea Ice near Lowest Recorded Levels -- Melting of the Greenland Ice Sheet -- Melting and Thickening of Ice in Antarctica -- No Melting of Some Permanent Ice Fields -- Contributions of Melting Ice and Warming Oceans to Sea Level Rise -- Hydrological Changes in the Western United States -- Observed Ecological Impacts of Climate Change -- WITHOUT FURTHER GHG MITIGATION POLICIES, GHG EMISSIONS WILL GROW -- PROJECTIONS OF FUTURE CLIMATE -- CONCERN ABOUT ABRUPT "TIPPING POINTS" IN THE CLIMATE SYSTEM.

PROJECTIONS OF FUTURE IMPACTS.