Environmental Physics

Sustainable Energy and Climate Change

Egbert Boeker, Rienk van Grondelle

• Editore: Wiley
• Anno: 2011
• ISBN:
  9781119975199
• Edizione: 3
• Argomento: Physical Sciences
• Categoria: Physics

This thoroughly revised and updated third edition focuses on the utilization of sustainable energy and mitigating climate change, serving as an introduction to physics in the context of societal problems. A distinguishing feature of the text is the discussion of spectroscopy and spectroscopic methods as a crucial means to quantitatively analyze and monitor the condition of the environment, the factors determining climate change, and all aspects of energy conversion.

This textbook will be invaluable to students in physics and related subjects, and supplementary materials are available on a companion website: http://www.nat.vu.nl/environmentalphysics
Instructor support material is available at: http://booksupport.wiley.com

1

Introduction

Physical science is a fascinating subject. Mechanics, quantum physics, electrodynamics, to name a few, present a coherent picture of physical reality. The present book aims at inspiring students with the enthusiasm the authors experienced while working in the field.

The work of the physical scientist always takes place in a social context. Ultimately, the scientist has to contribute to society, sometimes by increasing our knowledge of fundamental processes, more often by employing his or her skills in industry, a hospital, a consultancy firm or teaching. In the majority of cases the scientist contributes by tackling societal problems with a physics aspect or by educating students in understanding the strengths and limitations of the physics approach.

The text Environmental Physics focuses on two problems where physical scientists can contribute to make them manageable. The first is the need for a safe and clean supply of energy now and in the future, the second is the way to deal with the forecasted climate change. The major part of the text deals particularly with the physics aspects of these two problems. A brief discussion of the social context is given below with a section on the contribution of science. Science can point out the physical consequences of political choices, or of not making choices, but the decisions themselves should be taken through the political process. A more comprehensive discussion of the societal context is given in the last chapter of this book.

1.1 A Sustainable Energy Supply

The concept ‘sustainable development ’ became well known by the work of the World Commission on Environment and Development, acting by order of the General Assembly of the United Nations. In 1987 it defined sustainable development as ([1], p. 8):

Meeting the needs of the present generations without compromising the ability of future generations to meet their own needs.

This is not a physics definition, as the meaning of ‘needs’ is rather vague. Does it imply an expensive car, a motorboat and a private plane for everybody? The definition leaves this open. In the political arena the precise meaning of ‘needs’ is still to be decided. Still, the concept forces one to take into account the needs of future generations and rejects squandering our resources. Indeed, sustainable development, the World Commission emphasized, implies that we should be careful with natural resources and protect the natural environment.

Since 1987 many governments have put the goal of a ‘sustainable society’ in their policy statements. Besides protection of the environment and a safe energy supply it then comprises objectives like good governance, social coherence, a reasonable standard of living. In this book we focus on a sustainable energy supply and adapt the 1987 definition as follows:

A sustainable energy supply will meet the energy needs of the present generations without compromising the ability of future generations to meet their own energy needs. The environmental consequences of energy conversion should be such that present and future generations are able to cope.

Like with the previous definition the precise meaning of this statement is the subject of political debate. From a physics point of view one may make the following comments:

1. An energy supply based on fossil fuels is not sustainable. The resources of coal, oil and gas are limited, as will be illustrated in Chapter 9. So in time other energy sources will be required. In the meantime the environmental consequences of fossil fuel combustion should be controlled.

2. Renewable energy sources like solar energy, wind energy or bio fuels may be sustainable. Their ultimate source, solar irradiation, is inexhaustible on a human time scale. To be sure of the sustainability of renewable energy sources, one has to perform a life-cycle analysis: analyse the use of energy and materials of the equipment and their environmental consequences from cradle to grave. This book will provide building blocks for such an analysis.

3. It is under debate whether nuclear fission power is sustainable. The resources of 235U, the main nuclear fuel, are large, but limited. Also, during the fission process many radioactive materials are produced. Proponents of nuclear power argue that most of these ‘waste’ materials may be used again as fuel and the remainder may be stored; in practice, it is claimed, nuclear fission power would be ‘virtually sustainable’. Power from nuclear fusion may be sustainable, but its commercial exploitation is still far off.

Governments all over the world are stimulating renewable energies. Not only because of their sustainability. Another strong reason is the security of energy supply. This requires diversification of energy sources. Fossil fuels, especially oil and gas, are unevenly distributed over the world. Industrial countries do not want to be too much dependent on the willingness of other countries to supply them with oil and gas. One may put forward that solar irradiation is unevenly distributed as well, but even at moderate latitudes the irradiation is substantial and the wind blows everywhere.

Apart from these considerations, the combustion of fossil fuels produces CO2, which has climatic consequences, to be discussed in the next section.

1.2 The Greenhouse Effect and Climate Change

In the simplest calculation the temperature of the earth is determined by the solar radiation coming in and the infrared (IR) radiation leaving the earth, or

(1.1)

The amount of radiation entering the atmosphere per [m2] perpendicular to the radiation is called S, the total solar irradiance or solar constant in units [Wm−2] = [J s−1 m−2]. Looking at the earth from outer space it appears that a fraction a, called the albedo, is reflected back. As illustrated in Figure 1.1, an amount (1−a)S penetrates down to the surface. With earth radius R the left of Eq. (1.1) reads (1 − a)SπR2.

Figure 1.1 Solar radiation is entering the atmosphere from the left, S [Wm−2]. A fraction a, called the albedo, is reflected back.

In order to make an estimate of the right-hand side of Eq. (1.1) we approximate the earth as a black body with temperature T. A black body is a hypothetical body, which absorbs all incoming radiation, acquires a certain temperature T and emits its radiation according to simple laws, to be discussed in Chapter 2. At present the student should accept that according to Stefan–Boltzmann's law a black body produces outgoing radiation with intensity σT4 [Wm−2]. The total outgoing radiation from the earth then becomes σT4 × 4πR2. Substitution in Eq. (1.1) gives:

(1.2)

or

(1.3)

Numerical values of σ,R and S are given in Appendix A. For albedo a one finds from experiments a=0.30. Substitution gives T=255 [K], which is way below the true average earth surface temperature of 15 [°C] = 288 [K]. The difference of 33 [°C] is due to the greenhouse effect, for which the earth's atmosphere is responsible.

As will be shown later, the emission spectrum of the sun peaks at a wavelength of 0.5 [μm], whereas the earth's emission spectrum peaks at 10 [μm], the far IR. Several gases in our atmosphere, the so-called greenhouse gases, absorb strongly in the IR. In that way a large part of the solar radiation reaches the surface, but the emitted IR radiation has difficulty in escaping. The same effect happens in a greenhouse, hence the name.

It will be discussed later how human activities contribute to the greenhouse effect by increasing the concentration of greenhouse gases like CO2, tropospheric O3, N2O, CH4 and many HFCs...

Indice dei contenuti

• Cover
• Title Page
• Copyright
• Preface
• Acknowledgements
• Chapter 1: Introduction
• Chapter 2: Light and Matter
• Chapter 3: Climate and Climate Change
• Chapter 4: Heat Engines
• Chapter 5: Renewable Energy
• Chapter 6: Nuclear Power
• Chapter 7: Dispersion of Pollutants
• Chapter 8: Monitoring with Light
• Chapter 9: The Context of Society
• Appendix A: Physical and Numerical Constants
• Appendix B: Vector Algebra
• Appendix C: Gauss, Delta and Error Functions
• Appendix D: Experiments in a Student's Lab
• Appendix E: Web Sites
• Appendix F: Omitted Parts of the Second Edition
• Color Plate
• Index