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Foreword xiii Acknowledgements xv About the companion website xvii Introduction 1 PART I: THE CLIMATE ENGINE OF THE EARTH: ENERGY 5 1. Why are there many different climates on Earth? 7 2. Different climates . . . such diversity of life 11 2.1. The different climates on Earth 11 2.2. Climates, biomes and biodiversity 13 2.3. Climate and society 17 3. From a patchwork of climates to an average climate 19 3.1. Temperature and thermal equilibrium 19 3.2. The average temperature of the Earth???s surface 21 3.3. Precipitation 24 3.4. Wind 25 3.5. Three major items in energy consumption 26 4. The global mean climate 27 4.1. The Sun, source of energy 27 4.2. The energy equilibrium at the Earth???s surface 28 5. Atmosphere and ocean: key factors in climate equilibrium 33 5.1. Driving forces 34 5.2. The atmosphere 34 5.3. The oceans 42 5.4. Heat transport from the Equator to the poles 51 Part I: Summary 53 Part I: Notes 54 Part I: Further reading 54 PART II: MORE ON THE ENERGY BALANCE OF THE PLANET 55 6. Thermal radiation, solar and terrestrial radiation 57 6.1. Thermal radiation from a black body 57 6.2. The laws of black??]body radiation 58 6.3. Solar and terrestrial radiation 59 7. The impact of the atmosphere on radiation 61 7.1. Scattering and reflection 61 7.2. Absorption by a gas ??? the cut??]off approximation 62 7.3. Absorption of solar and terrestrial radiation by atmospheric gases 64 7.4. Direct transfer by the atmosphere 68 7.5. Major atmospheric constituents involved in radiative transfer 69 8. Radiative transfer through the atmosphere 73 8.1. Three radiative mechanisms that heat or cool the Earth???s surface 73 8.2. The greenhouse effect 78 8.3. Radiative transfer: the roles of the different constituents 83 8.4. The radiation balance of the Earth 86 9. The energy balance 87 9.1. The energy balance at the surface of the Earth in the single??]layer model 87 9.2. The Earth???s energy balance at equilibrium 89 9.3. The impact of human activity 91 9.4. The present unbalanced global energy budget 91 10. Climate forcing and feedback 93 10.1. Climate forcing 93 10.2. Feedbacks 95 10.3. Climate sensitivity 98 11. Climate modelling 99 11.1. The Energy Balance and Radiative???Convective Models 99 11.2. Three–dimensional Atmosphere Global Circulation Models 101 11.3. Three–dimensional models: ever–increasing refinements 103 11.4. Climate models ??? what for? 104 Part II. Summary 105 Part II. Notes 106 Part II. Further reading 107 PART III: THE DIFFERENT CAUSES OF CLIMATE CHANGE 109 12. The choice of approach 111 13. The Sun???s emission 115 13.1. The impact on the climate 115 13.2. How emission varies 115 13.3. What are the consequences? 117 14. The position of the Earth with respect to the Sun 119 14.1. An overview 119 14.2. Irradiance, determined by orbital parameters 120 14.3. Changes in obliquity: the impact on the seasons 120 14.4. Changes in the Earth???s orbit and eccentricity: the impact on the Earth???Sun distance 122 14.5. Precession of the axis of rotation: the impact on the Earth???Sun distance at different seasons 124 14.6. Changes in irradiance 127 15. The composition of the atmosphere 129 15.1. The effect on the climate: the mechanism 129 15.2. How the composition has changed, and why 130 15.3. What are the consequences? 133 16. Heat transfer from the Equator to the poles 135 16.1. The impact on the climate: the mechanism 135 16.2. How and why can the transfer vary? 135 16.3. What are the consequences? 136 17. Oscillations due to ocean???atmosphere interactions 137 17.1. The impact on the climate: the mechanism 137 17.2. The El Niño Southern Oscillation and trade wind fluctuations 138 17.3. The North Atlantic and Arctic Oscillations 142 Part III. Summary 145 Part III. Notes 146 Part III. Further reading 147 PART IV: LEARNING FROM THE PAST ??? 149 18. Memory of the distant past 151 18.1. Over billions of years ??? 151 18.2. The past tens of millions of years: slow cooling 152 18.3. The entry of Northern Hemisphere glaciations 156 19. Since 2.6 million years ago: the dance of glaciations 161 19.1. The archives of the dance 161 19.2. The glacial???interglacial cycles 168 19.3. Glacials and interglacials: very different climate stages 169 19.4. Glacials and interglacials: similar but never identical 173 19.5. Abrupt climate changes in the last climate cycle 174 20. Glacial???interglacial cycles and the Milankovitch theory 181 20.1. The leading role of the Northern Hemisphere 182 20.2. Seasonal irradiance, the key parameter in Quaternary glaciations 182 20.3. Two types of configuration 183 20.4. The climate in the past 250,000 years 184 20.5. Glacials and interglacials: similar situations, never identical 188 20.6. The energy budget: radiative forcing and feedback 189 21. The glaciation dance: consequences and lessons 191 21.1. The impact on life of glacial???interglacial cycles 191 21.2. Lessons to be drawn 196 21.3. When will the next glaciation come? 198 22. The past 12,000 years: the warm Holocene 201 22.1. The Holocene 201 22.2. Deciphering climate changes during the Holocene 202 22.3. Slow changes in irradiance (Timescale 1: millennia) 203 22.4. Slow cooling at middle and high latitudes in the Northern Hemisphere 203 22.5. Strong monsoon in the Early Holocene: the ???Green Sahara??? episode 206 22.6. Solar fluctuations (Timescale 2: centuries) 214 22.7. The Holocene and the birth of agriculture and animal husbandry 222 23. Global and regional fluctuations (Timescale 3: decades) 225 23.1. From global ??? 226 23.2. ??? to regional: the North Atlantic Oscillation 229 23.3. The Sun, the other source of change 230 24. Future warming and past climates 231 24.1. The global ???hot flush??? of 55 million years ago 231 24.2. Three million years ago 233 24.3. Warmer periods in the past 2 million years? 233 Part IV. Summary 235 Part IV. Notes 236 Part IV. Further reading 239 PART V: CLIMATE CHANGE IN RECENT YEARS 241 25. Recent climate change 243 25.1. Changes in temperature 243 25.2. Changes in precipitation, water vapour and extreme events 249 25.3. An overview of the past few decades 255 25.4. The impact of global warming: the key issue 255 26. The impact of global warming on the cryosphere 257 26.1. Sea ice, the ???canary??? of our planet 257 26.2. Changes in glaciers 261 26.3. Ice??]sheet changes 264 26.4. Changes in frozen soils 267 26.5. Freeze??]up and snow cover 271 27. The impact of warming on the ocean 273 27.1. Change in sea level 274 27.2. Regional changes in ocean salinity 278 27.3. Is deep ocean circulation slowing? 279 27.4. Changes in dissolved carbon dioxide and ocean acidification 280 27.5. In summary: consistency over the globe 283 28. The impact of warming on the biosphere 285 28.1. Ongoing changes 285 28.2. Oceans 286 28.3. Land 289 28.4. Portents of dysfunction 295 29. Warming in the 20th century: natural or human??]induced? 297 29.1. The carbon cycle prior to the industrial era 298 29.2. The impact of human activity on the carbon cycle 305 29.3. Changes related to human activity 310 29.4. Natural causes: solar and volcanic activity 313 29.5. An overview of all the causes: the major role of human activity 314 Part V. Summary 320 Part V. Notes 321 Part V. Further reading 322 PART VI: CLIMATE IN THE 21ST CENTURY: DIFFERENT SCENARIOS 323 30. Two key factors 325 30.1. Greenhouse gas emissions 325 30.2. Population growth 328 31. Projections: economic scenarios and climate models 329 31.1. Successive steps in a projection 329 31.2. Climate models 331 32. Simulations: a survey 333 32.1. Long??]term scenarios 333 32.2. IPCC 2007 scenarios for the 21st century 336 32.3. IPCC 2013 scenarios for the 21st century 339 33. Future warming and its consequences 343 33.1. Global warming 343 33.2. The water cycle and precipitation 344 33.3. Extreme events 347 33.4. Snow and ice 347 33.5. The sea level 348 33.6. Ocean acidification 349 33.7. Climate predictions: what degree of confidence? 350 33.8. In summary, the future is already with us 354 34. The choice 355 34.1. Can future warming be counteracted naturally? 355 34.2. Which choice of scenario? 356 34.3. Global warming: no more than 2°C 360 34.4. The ???Triple Zero??? challenge 360 35. Climate change in the present state of the planet 363 35.1. Environmental degradation 363 35.2. Depletion of energy resources 364 35.3. Inexorable world population growth? 364 35.4. A new type of development? 364 Part VI. Summary 366 Part VI. Notes 367 Part VI. Further reading 368 Conclusion 369 References 373 Index 383