### IPCC Fourth A**ssessment Report: Climate Change 2007**

**Climate Change 2007: Working Group I: The Physical Science Basis** Contents 2 

### Chapter 2: Changes in Atmospheric Constituents and in Radiative Forcing Executive Summary 2.1 Introduction and Scope 2.2 Concept of Radiative Forcing FAQ 2.1 How do Human Activities Contribute to Climate Change and How do They Compare with Natural Influences? 2.3 Chemically and Radiatively Important Gases 2.3.1 Atmospheric Carbon Dioxide 2.3.2 Atmospheric Methane 2.3.3 Other Kyoto Protocol Gases 2.3.4 Montreal Protocol Gases 2.3.5 Trends in the Hydroxyl Free Radical 2.3.6 Ozone 2.3.7 Stratospheric W ater Vapour 2.3.8 Observations of Long

- Lived Greenhouse Gas Radiative Effects 2.4 Aerosols 2.4.1 Introduction and Summary of the Third Assessment Report 2.4.2 Developments Related to Aerosol Observations 2.4.3 Advances in Modelling the Aerosol Direct Effect 2.4.4 Estimates of Aerosol Direct Radiative Forcing 2.4.5 Aerosol Influence on Clouds (Cloud Albedo Effect) 2.5 Anthropogenic Changes in Surface Albedo and the Surface Energy Budget 2.5.1 Introduction 2.5.2 Changes in Land Cover Since 1750 2.5.4 Radiative Forcing by Anthropogenic Surface Albedo Change: Black Carbon in Snow and Ice 2.5.5 Other Effe cts of Anthropogenic Changes in Land Cover 2.5.6 Tropospheric W ater Vapour from Anthropogenic Sources 2.5.7 Anthropogenic Heat Release 2.5.8 Effects of Carbon Dioxide Changes on Climate via Plant Physiology: ‘Physiological Forcing’ 2.6 Contrails and Aircraft

- Induced Cloudiness 2.6.1 Introduction 2.6.2 Radiative Forcing Estimates for Persistent Line

- Shaped Contrails 2.6.3 Radiative Forcing Estimates for Aviation

- Induced Cloudiness 2.6.4 Aviation Aerosols 2.7 Natural Forcings 2.7.1 Solar Variability 2.7.2 Explosive Volcanic Activity 2.8 Utility of Radiative Forcing 2.8.1 Vertical Forcing Patterns and Surface Energy Balance Changes 2.8.2 Spatial Patterns of Radiative Forcing 2.8.3 Alternative Methods of Calculating Radiative Fo rcing 2.8.4 Linearity of the Forcing

- Response Relationship 2.8.5 Efficacy and Effective Radiative Forcing2.8.6 Efficacy and the Forcing

- Response Relationship 2.9 Synthesis 2.9.1 Uncertainties in Radiative Forcing 2.9.2 Global Mean Radiative Forcing 2.9.3 Global Mean Radiative Forcing by Emission Precursor 2.9.4 Future Climate Impact of Current Emissions 2.9.5 Time Evolution of Radiative Forcing and Surface Forcing 2.9.6 Spatial Patterns of Radiati ve Forcing and Surface Forcing 2.10 Global Warming Potentials and Other Metrics for Comparing Different Emissions 2.10.1 Definition of an Emission Metric and the Global W arming Potential 2.10.2 Direct Global W arming Potentials 2.10.3 Indirect GWPs 2.10.4 New Alternative Metrics for Assessing Emissions References 

### Coordinating Lead Authors: Piers Forster (UK), Venkatachalam Ramaswamy (USA)


### Lead Authors: Paulo Artaxo (Brazil), Terje Berntsen (Norway), Richard Betts (U K), David W . Fahey (USA), James Haywood (UK), Judith Lean (USA), David C. Lowe (New Zealand), Gunnar Myhre (Norway), John Nganga (Kenya), Ronald Prinn (USA, New Zealand), Graciela Raga (Mexico, Argentina), Michael Schulz (France, Germany), Robert Van Dorla nd (Netherlands) 

### Contributing Authors: G. Bodeker (New Zealand), O. Boucher (UK, France), W .D. Collins (USA), T.J. Conway (USA), E. Dlugokencky (USA), J.W . Elkins (USA), D. Etheridge (Australia), P. Foukal (USA), P. Fraser (Australia), M. Geller (USA), F. Joos (Switzerland), C.D. Keeling (USA), R. Keeling (USA), S. Kinne (Germany), K. Lassey (New Zealand), U. Lohmann (Switzerland), A.C. Manning (UK, New Zealand), S. Montzka (USA), D. Oram (UK), K. O’Shaugh nessy (New Zealand), S. Piper (USA), G.

- K. Plattner (Switzerland), M. Ponater (Germany), N. Ramankutty (USA, India), G. Reid (USA), D. Rind (USA), K. Rosenlof (USA), R. Sausen (Germany), D. Schwarzkopf (USA), S.K. Solanki (Germany, Switzerland), G. Stenc hikov (USA), N. Stuber (UK, Germany), T. Takemura (Japan), C. Te xtor (France, Germany), R. W ang (USA), R. W eiss (USA), T. W horf (USA)


### Review Editors: Teruyuki Nakajima (Japan), Veerabhadran Ramanathan (USA) 

### This chapter should be cited as: Forster, P. , V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W . Fahey, J. Haywood, J. Lean, D.C. Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland, 2007: Changes in Atmospheric Constituents and in Radiative Forcing. In: Climate Change 2007: The Physical Science Basis. Contribution of Wo rking Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge Un iversity Press, Cambridge, United Kingdom and New York, NY, USA.