Climate Change

Observed impacts on Planet Earth

Trevor Letcher, Trevor M. Letcher

• Publisher: Elsevier Science
• Year: 2009
• Print ISBN: 9780444533012
• eBook ISBN: 9780080933030
• Topic: Physical Sciences
• Subtopic: Global Warming & Climate Change

The climate of the Earth is always changing. As the debate over the implications of changes in the Earth's climate has grown, the term climate change has come to refer primarily to changes we've seen over recent years and those which are predicted to be coming, mainly as a result of human behavior. This book serves as a broad, accessible guide to the science behind this often political and heated debate by providing scientific detail and evidence in language that is clear to both the non-specialist and the serious student. - Provides all the scientific evidence for and possible causes of climate change in one book - Written by expert scientists working in the field - Logical, non-emotional conclusions - A source book for the latest findings on climate change

Chapter 1. The Role of Atmospheric Gases in Global Warming

Richard P. Tuckett

School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom

1 Introduction

2 Origin of the Greenhouse Effect:‘Primary’ and ‘Secondary’Effects

3 The Physical ChemistryProperties of Greenhouse Gases

4 The Lifetime of a GreenhouseGas in the Earth’s Atmosphere

5 General Comments onLong-Lived Greenhouse Gases

6 Conclusion

Acknowledgements

References

1. Introduction

If the general public in the developed world is confused about what the greenhouse effect is, what the important greenhouse gases are, and whether greenhouse gases really are the predominant cause of the recent rise in temperature of the earth's atmosphere, it is hardly surprising. Nowadays, statements by one scientist are often immediately refuted by another, and both tend to state their claims with almost religious fervour. Furthermore, politicians and the media have not helped. It is only 14 a (years) ago that the newly appointed Secretary of State for the Environment in the United Kingdom made the cardinal sin of confusing the greenhouse effect with ozone depletion by saying they had the same scientific causes. (In retrospect, John Gummer was closer to the truth than he realised, in that one class of chemicals, the chlorofluorocarbons (CFCs), are both the principal cause of ozone depletion and are major greenhouse gases, but these two facts are scientifically unrelated.) Furthermore, to many, even in the respectable parts of the media, ‘greenhouse gases’ are two dirty words. In fact, nothing could be further from the truth, in that there has always been a greenhouse effect operative in the earth's atmosphere. Without it we would inhabit a very cold planet, and not exist in the hospitable temperature of 290–300 K.

The purpose of this opening chapter of this book is to explain in simple terms what the greenhouse effect is, what its origins are and what the properties of greenhouse gases are. I will restrict this chapter to an explanation of the physical chemistry of greenhouse gases and the greenhouse effect, and not delve too much into the politics of ‘what should or should not be done’. However, one simple message to convey at the onset is that the greenhouse effect is not just about concentration levels of carbon dioxide (CO₂), and it is too simplistic to believe that all our problems will be solved, if we can reduce CO₂ concentrations by x% in y years. Shine [1] has also commented many times that there is much more to the greenhouse effect than carbon dioxide levels.

2. Origin of the Greenhouse Effect: ‘Primary’ and ‘Secondary’ Effects

The earth is a planet in dynamic equilibrium, in that it continually absorbs and emits electromagnetic radiation. It receives ultra-violet and visible radiation from the sun, it emits infra-red radiation and energy balance says that ‘energy in’ must equal ‘energy out’ for the temperature of the planet to be constant. This equality can be used to determine what the average temperature of the planet should be. Both the sun and the earth are black-body emitters of electromagnetic radiation. That is, they are masses capable of emitting and absorbing all frequencies (or wavelengths) of electromagnetic radiation uniformly. The distribution curve of emitted energy per unit time per unit area versus wavelength for a black body was worked out by Planck in the first part of the twentieth century, and is shown pictorially in Fig. 1. Without mathematical detail, two points are relevant. First, the total energy emitted per unit time integrated over all wavelengths is proportional to (T/K)⁴. Second, the wavelength of the maximum in the emission distribution curve varies inversely with (T/K), that is, λ_max α (T/K)⁻¹. These are Stefan's and Wien's Laws, respectively. Comparing the black-body curves of the sun and the earth, the sun emits UV/visible radiation with a peak at ca. 500 nm characteristic of T_sun = 5780 K. The temperature of the earth is a factor of 20 lower, so the earth's black-body emission curve peaks at a wavelength which is 20 times longer or ca. 10 μm. Thus the earth emits infra-red radiation with a range of wavelengths spanning ca. 4–50 μm, with the majority of the emission being in the range 5–25 μm (or 400–2000 cm⁻¹).

Figure 1 Black-body emission curves from the sun (T ∼ 5780 K) and the earth (T ∼ 290 K), showing the operation of Wien's Law that λmax α (1/T). The two graphs are not to scale.

The solar flux energy intercepted per second by the earth's surface from the sun's emission can be written as F_s(1−A)πR_e², where F_s is the solar flux constant outside the Earth's atmosphere (1368 J·s⁻¹·m⁻²), R_e is the radius of the Earth (6.38 × 10⁶ m), and A is the earth's albedo, corresponding to the reduction of incoming solar flux by absorption and scattering of radiation by aerosol particles (average value 0.28). The infra-red energy emitted per second from the earth's surface is 4πR_e²sT_e⁴, where s is St...

Table of contents

• Cover Image
• Table of Contents
• Copyright
• Foreword
• Preface
• Contributors
• Introduction
• Chapter 1. The Role of Atmospheric Gases in Global Warming
• Chapter 2. The Role of Widespread Surface Solar Radiation Trends in Climate Change
• Chapter 3. The Role of Space Weather and Cosmic Ray Effects in Climate Change
• Chapter 4. The Role of Volcanic Activity in Climate and Global Change
• Chapter 5. The Role of Variations of the Earth's Orbital Characteristics in Climate Change
• Chapter 6. A Geological History of Climate Change
• Chapter 7. Changes in the Atmospheric Circulation as Indicator of Climate Change
• Chapter 8. Weather Pattern Changes in the Tropics and Mid-Latitudes as an Indicator of Global Changes
• Chapter 9. Bird Ecology as an Indicator of Climate and Global Change
• Chapter 10. Mammal Ecology as an Indicator of Climate Change
• Chapter 11. Climate Change and Temporal and Spatial Mismatches in Insect Communities
• Chapter 12. Sea Life (Pelagic and Planktonic Ecosystems) as an Indicator of Climate and Global Change
• Chapter 13. Changes in Coral Reef Ecosystems as an Indicator of Climate and Global Change
• Chapter 14. Changes in Marine Biodiversity as an Indicator of Climate Change
• Chapter 15. Intertidal Indicators of Climate and Global Change
• Chapter 16. Plant Ecology as an Indicator of Climate and Global Change
• Chapter 17. The Impact of Climate and Global Change on Crop Production
• Chapter 18. Rising Sea Levels as an Indicator of Global Change
• Chapter 19. Sea Temperature Change as an Indicator of Global Change
• Chapter 20. Ocean Current Changes as an Indicator of Global Change
• Chapter 21. Ocean Acidification as an Indicator for Climate Change
• Chapter 22. Ice Sheets
• Chapter 23. Lichens as an Indicator of Climate and Global Change
• Chapter 24. Coastline Degradation as an Indicator of Global Change
• Chapter 25. Plant Pathogens as Indicators of Climate Change
• Index