This book is designed for first- and second-year university students (and their instructors) in earth science, environmental science, and physical geography degree programmes worldwide. The summaries at the end of each section constitute essential reading for policy makers and planners. It provides a simple but masterly account, with a minimum of equations, of how the Earth’s climate system works, of the physical processes that have given rise to the long sequence of glacial and interglacial periods of the Quaternary, and that will continue to cause the climate to evolve. Its straightforward and elegant description, with an abundance of well chosen illustrations, focuses on different time scales, and includes the most recent research in climate science by the United Nations Intergovernmental Panel on Climate Change (IPCC). It shows how it is human behaviour that will determine whether or not the present century is a turning point to a new climate, unprecedented on Earth in the last several million years.
Table of Contents
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 blackÂ]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 cutÂ]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 singleÂ]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. IceÂ]sheet changes 264
26.4. Changes in frozen soils 267
26.5. FreezeÂ]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 humanÂ]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. LongÂ]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
