Climate Change

Marie-Antoinette Mélières, Docteur d’Etat in physics, taught basic physics and, later, climate and environmental science at Joseph Fourier University of Grenoble 1 and at the University of Savoie. Her research has covered various areas ranging from molecular spectroscopy and atmospheric physics to environmental and climate science. In 1995 she established the newsletter Global Change, published by the French National Committee on Climate Change, under the authority of the Academy of Sciences. The Committee is the French branch of the four international programs IGBP, WCRP, IHDP and Diversitas. She continued to edit this publication until 2008. Chloé Maréchal, PhD, geochemist, is Maître de Conférences in the Observatoire des Sciences de l’Univers at Université Claude Bernard Lyon 1, where she teaches Earth Sciences at first university degree level and at Masters level. In her research into the biogeochemical cycles of copper and zinc in the Earth's outer layers, she established a protocol for using isotopes of these elements by plasma-source mass spectrometry and investigated their isotopic fractionation in marine sediments, as well as in soils affected by human activity. She also worked on the geochemical cycle of boron, using its isotopic signal in marine biogenic carbonates as tool in paleo-oceanographic reconstructions.

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