1 Chapter 7: Couplings Between Changes in the Climate System And
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First Order Draft Chapter 7 IPCC WG1 Fourth Assessment Report 1 2 Chapter 7: Couplings Between Changes in the Climate System and Biogeochemistry 3 4 Coordinating Lead Authors: Guy Brasseur, Kenneth Denman 5 6 Lead Authors: Amnat Chidthaisong, Philippe Ciais, Peter Cox, Robert Dickinson, Didier Hauglustaine, 7 Christoph Heinze, Elisabeth Holland, Daniel Jacob, Ulrike Lohmann, Srikanthan Ramachandran, Pedro 8 Leite da Silva Diaz, Steven Wofsy, Xiaoye Zhang 9 10 Contributing Authors: David Archer, V. Arora, John Austin, D. Baker, Joe Berry, Gordon Bonan, Philippe 11 Bousquet, Deborah Clark, V. Eyring, Johann Feichter, Pierre Friedlingstein, Inez Fung, Sandro Fuzzi, 12 Sunling Gong, Alex Guenther, Ann Henderson-Sellers, Andy Jones, Bernd Kärcher, Mikio Kawamiya, 13 Yadvinder Malhi, K. Masarie, Surabi Menon, J. Miller, P. Peylin, A. Pitman, Johannes Quaas, P. Rayner, 14 Ulf Riebesell, C. Rödenbeck, Leon Rotstayn, Nigel Roulet, Chris Sabine, Martin Schultz, Michael Schulz, 15 Will Steffen, Steve Schwartz, J. Lee-Taylor, Yuhong Tian, Oliver Wild, Liming Zhou. 16 17 Review Editors: Kansri Boonpragob, Martin Heimann, Mario Molina 18 19 Date of Draft: 12 August 2005 20 21 Notes: This is the TSU compiled version 22 23 24 Table of Contents 25 26 Executive Summary ............................................................................................................................................................... 3 27 7.1 Introduction.................................................................................................................................................................... 6 28 7.1.1 Terrestrial Ecosystems and the Climate System.............................................................................................. 6 29 7.1.2. The Carbon Cycle and the Climate System .................................................................................................... 7 30 7.1.3. Reactive Gases and the Climate System ......................................................................................................... 8 31 7.1.4 Aerosol Particles and the Climate System....................................................................................................... 9 32 7.2 The Changing Land Surface and Climate..................................................................................................................... 9 33 7.2.1 Introduction to Land Climate Response from Human Activities .................................................................... 9 34 7.2.2 How Does Land Surface Mediate Climate Change?....................................................................................... 9 35 7.2.3 What Has Been Learned About Land Model Structures Since the TAR? ..................................................... 12 36 7.2.4 How Can We Quantitatively Relate Land Climate Changes to Atmospheric Inputs and Structural 37 Change?....................................................................................................................................................................... 13 38 7.2.5 Functioning of System Models - Improving Their Basis for Quantitative Evaluation of Impacts of Land 39 Changes ...................................................................................................................................................................... 16 40 7.3 The Carbon Cycle and the Climate System ................................................................................................................ 17 41 7.3.1 Contemporary Carbon Budget....................................................................................................................... 17 42 7.3.2 Carbon Cycle Processes ................................................................................................................................ 19 43 Box 7.1: Marine Carbon Chemistry and Ocean Acidification............................................................................................ 23 44 7.3.3 Interannual and Regional Variation in Carbon Fluxes Inferred from Observations.................................. 32 45 7.3.4 Coupled Climate-Carbon Cycle Projections................................................................................................. 38 46 Question 7.1: Are the Increases in Atmospheric Carbon Dioxide and Other Greenhouse Gases During the Industrial Era 47 Caused by Human Activities?..................................................................................................................................... 44 48 7.4 Reactive Gases and the Climate System..................................................................................................................... 45 49 7.4.1 Methane (CH4)................................................................................................................................................ 45 50 7.4.2. Nitrogen Compounds...................................................................................................................................... 50 51 7.4.3. Molecular Hydrogen ...................................................................................................................................... 52 52 7.4.4 Global Tropospheric Ozone........................................................................................................................... 53 53 7.4.5. The Hydroxyl Radical (OH)........................................................................................................................... 57 54 7.4.6 Stratospheric Ozone and Climate .................................................................................................................. 61 55 7.5 Aerosol Particles and the Climate System.................................................................................................................. 62 56 7.5.1 What Major Climatic Factors Control Natural Aerosol Emissions and Burdens?...................................... 63 57 7.5.2 How Do Aerosols (Indirect Effects) Modify Clouds and Precipitation? ...................................................... 65 58 7.5.3 How Are Changes in Aerosols/Clouds Affecting Processes at the Earth’s Surface?................................... 70 59 7.5.4 How Are Aerosols Affecting Circulation Patterns? ...................................................................................... 72 60 7.6 Concluding Remarks ................................................................................................................................................... 74 Do Not Cite or Quote 7-1 Total pages: 119 First Order Draft Chapter 7 IPCC WG1 Fourth Assessment Report 1 Box 7.2: Effects of Climate Change on Air Quality ........................................................................................................... 74 2 References ............................................................................................................................................................................ 77 3 Tables..................................................................................................................................................................................118 4 Do Not Cite or Quote 7-2 Total pages: 119 First Order Draft Chapter 7 IPCC WG1 Fourth Assessment Report 1 Executive Summary 2 3 Biogeochemical cycles interact with the climate system over a variety of temporal and spatial scales. 4 Nonlinear interactions involving physical, chemical and biological processes within or between the different 5 compartments of the Earth system could amplify (positive feedbacks) or attenuate (negative feedbacks) the 6 disturbances produced by human activities. The response of the climate system to anthropogenic 7 perturbations is therefore expected to be more complex and more chaotic than a simple cause-effect 8 relationship; it involves reciprocal interactions with the land surface, the carbon cycle, reactive gases and 9 aerosol particles. 10 11 The Land Surface and Climate 12 13 • Changes in temperature, moisture, and solar irradiance as well as atmospheric composition will affect 14 the distribution and functioning of terrestrial ecosystems. The ecosystem response, in turn, will alter the 15 momentum, energy, and water balance of the atmosphere, as well as the cycling of carbon, methane, dust 16 and other atmospheric trace constituents. 17 • Changes in land vegetation, soils, and water cycle resulting from human activities can affect regional 18 climate through shifts in cloudiness, surface temperatures, and radiation. 19 • Land use changes have contributed ~35% of the buildup of atmospheric CO2 since preindustrial times – 20 indicating that future scenarios and model projections must account for land use change. 21 • Many modelling studies demonstrate that changing land cover can have local and regional climate 22 impacts that are comparable in magnitude with temperature and precipitation changes observed over the 23 last several decades as reported in Chapter 3. 24 • New developments in dynamic vegetation schemes and coupled climate-carbon models have shown that 25 the physiological forcing of stomatal closure can contribute 20% to the rainfall reduction in the Amazon 26 associated with rising atmospheric CO2 levels. 27 28 The Carbon Cycle and Climate 29 30 • The average increase in atmospheric CO2, determined from the global CMDL network, was 1.88 ppm 31 yr-1, or 3.99 Pg-C yr-1 for 2000–2004. 32 • The land was a large source of CO2 to the atmosphere in 1988 because