ney September,October, 2009 2009 December 7, 2009 i Acknowledgments EPA authors and contributors: Benjamin DeAngelo, Jason Samenow, Jeremy Martinich, Doug Grano, Dina Kruger, Marcus Sarofim, Lesley Jantarasami, William Perkins, Michael Kolian, Melissa Weitz, Leif Hockstad, William Irving, Lisa Hanle, Darrell Winner, David Chalmers, Brian Cook, Chris Weaver, Susan Julius, Brooke Hemming, Sarah Garman, Rona Birnbaum, Paul Argyropoulos, Al McGartland, Alan Carlin, John Davidson, Tim Benner, Carol Holmes, John Hannon, Jim Ketcham-Colwill, Andy Miller, and Pamela Williams. Federal expert reviewers Virginia Burkett, USGS; Phil DeCola; NASA (on detail to OSTP); William Emanuel, NASA; Anne Grambsch, EPA; Jerry Hatfield, USDA; Anthony Janetos; DOE Pacific Northwest National Laboratory; Linda Joyce, USDA Forest Service; Thomas Karl, NOAA; Michael McGeehin, CDC; Gavin Schmidt, NASA; Susan Solomon, NOAA; and Thomas Wilbanks, DOE Oak Ridge National Laboratory. Other contributors: Eastern Research Group (ERG) assisted with document editing and formatting. Stratus Consulting also assisted with document editing and formatting. ii Table of Contents Executive Summary..............................................................................................................ES-1 I. Introduction 1. Introduction and Background ..................................................................................................... 2 a. Scope and Approach of This Document.................................................................................... 2 b. Data and Scientific Findings Considered by EPA..................................................................... 4 c. Roadmap for This Document .................................................................................................... 8 II. Greenhouse Gas Emissions 2. Greenhouse Gas Emissions and Concentrations ...................................................................... 11 a. U.S. and Global Greenhouse Gas and Selected Aerosol Emissions........................................ 11 b. Lifetime of Greenhouse Gases in the Atmosphere.................................................................. 16 c. Historic and Current Global Greenhouse Gas Concentrations ............................................... 17 III. Global and U.S. Observed and Projected Effects From Elevated Greenhouse Gas Concentrations 3. Direct Effects of Elevated Greenhouse Gas Concentrations.................................................... 21 4. Radiative Forcing and Observed Climate Change ................................................................... 23 a. Radiative Forcing Due to Greenhouse Gases and Other Factors ............................................ 23 b. Global Changes in Temperature.............................................................................................. 26 c. U.S. Changes in Temperature.................................................................................................. 32 d. Global Changes in Precipitation.............................................................................................. 34 e. U.S. Changes in Precipitation.................................................................................................. 35 f. Global Sea Level Rise and Ocean Heat Content ..................................................................... 35 g. U.S. Sea Level Rise................................................................................................................. 37 h. Global Ocean Acidification..................................................................................................... 38 i. Global Changes in Physical and Biological Systems .............................................................. 38 j. U.S. Changes in Physical and Biological Systems.................................................................. 41 k. Global Extreme Events............................................................................................................ 43 l. U.S. Extreme Events ............................................................................................................... 44 5. Attribution of Observed Climate Change to Anthropogenic Greenhouse Gas Emissions at the Global and Continental Scale ............................................................................................... 47 a. Attribution of Observed Climate Change to Anthropogenic Emissions ................................. 47 b. Attribution of Observed Changes in Physical and Biological Systems................................... 53 6. Projected Future Greenhouse Gas Concentrations and Climate Change .............................. 55 a. Global Emissions Scenarios and Associated Changes in Concentrations and Radiative Forcing .................................................................................................................................... 55 b. Projected Changes in Global Temperature, Precipitation Patterns, Sea Level Rise, and Ocean Acidification............................................................................................................................ 63 c. Projected Changes in U.S. Temperature, Precipitation Patterns, and Sea Level Rise............. 68 d. Cryosphere (Snow and Ice) Projections, Focusing on North America and the United States. 72 e. Extreme Events, Focusing on North America and the United States...................................... 73 iii f. Abrupt Climate Change and High-Impact Events................................................................... 75 g. Effects on/from Stratospheric Ozone ...................................................................................... 78 h. Land Use and Land Cover Change.......................................................................................... 80 IV. U.S. Observed and Projected Human Health and Welfare Effects from Climate Change 7. Human Health .............................................................................................................................. 82 a. Temperature Effects ................................................................................................................ 83 b. Extreme Events........................................................................................................................ 85 c. Climate-Sensitive Diseases ..................................................................................................... 86 d. Aeroallergens........................................................................................................................... 88 8. Air Quality.................................................................................................................................... 89 a. Tropospheric Ozone ................................................................................................................ 89 b. Particulate Matter ................................................................................................................... 93 c. Health Effects Due to CO2-Induced Increases in Tropospheric Ozone and Particulate Matter… ................................................................................................................................ ..96 9. Food Production and Agriculture .............................................................................................. 97 a. Crop Yields and Productivity .................................................................................................. 98 b. Irrigation Requirements......................................................................................................... 100 c. Climate Variability and Extreme Events............................................................................... 101 d. Pests and Weeds .................................................................................................................... 101 e. Livestock ............................................................................................................................... 102 f. Freshwater and Marine Fisheries........................................................................................... 103 10. Forestry....................................................................................................................................... 104 a. Forest Productivity ............................................................................................................... 105 b. Wildfire and Drought Risk.................................................................................................... 106 c. Forest Composition ............................................................................................................... 108 d. Insects and Diseases .............................................................................................................. 108 11. Water Resources ........................................................................................................................ 110 a. Water Supply and Snowpack ................................................................................................ 110 b. Water Quality ........................................................................................................................ 113 c. Extreme Events...................................................................................................................... 115 d. Implications for Water Uses.................................................................................................