Contemporary Climatology

P.J. Robinson, Ann Henderson-Sellers

• Publisher: Routledge
• Year: 2014
• ISBN:
  9781317889540
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Geography
• Index: Geography

Now in its second edition, Climatology continues to provide an up-to-date stimulating and comprehensive guide to the nature of the earth's climate. It presents a synthesis of contemporary scientific ideas about atmospheric circulation. Topics covered include:
-Energy systems-The hydrological cycle-General circulation, local and regional climate-Application of climate information-Use of satellite observations

CHAPTER 1

The scope and controls of the climate

The envelope of air that surrounds the Earth affects us in many ways as we go about our day-to-day activities. Sometimes we respond to it almost unconsciously, as when we choose the type of clothes we will wear. At other times a conscious decision is needed: do we carry an umbrella today? On a longer time scale, our houses reflect the influence of climate, since, if winters are likely to be cold, we install a heating system. To alleviate hot summers, industrial societies install air conditioning, while non-industrial societies select building sites and designs that allow natural cooling. We predict future conditions when we decide what to plant in our gardens or fields, or when we schedule the time and place of our vacation. Institutions, as well as individuals, are influenced by the atmosphere. An electricity generating company must ensure that it has enough capacity to meet the demand on the coldest, or hottest, day. A water supply authority must plan so that it has enough storage to supply the needs during a long drought. A construction firm must determine the strongest winds likely to be encountered in order to build structures which can resist them.

Such problems, local and practical, and almost as old as civilisation itself, are climatological problems. More recently, climatological problems that are less visible and obvious, but more widespread, have arisen. These are associated with the human activities which are altering the composition of the Earth’s atmosphere and the nature of its surface, and which may be leading to changes in the climate of the whole globe. Solutions to these problems, whether long-standing and local, or newer and global, require predictions of future conditions. The provision of such predictions, through increased understanding of atmospheric processes, fuller descriptions of the planet’s climate, and better specification of the links between human activities and climate, is the aim of contemporary climatology.

As the range of climatological questions increases, so does the number of observations and analysis tools available to try to answer them. For many years the prime function of climatology was to synthesise the many observations of the ‘elements’ that constitute climate to provide a description of the varied climates of the Earth’s surface, and to analyse the results to gain insight into the processes controlling climate. Although the observations were mainly of surface conditions, and therefore could lead to only partial explanations of climate, much of the information we commonly associate with climate – monthly average temperature and monthly total precipitation, for example – derives from these observations. The scope of climatology over the last few decades has increased immensely. Satellite observations, providing three-dimensional and global coverage, have literally and figuratively transformed our viewpoint. Almost at the other extreme, the recent development of enhanced radar systems is now allowing analysis of clouds, wind and rain in very fine detail. These observational advances have forced an explicit realisation that there is a climate system in which the climate of a particular place is constantly changing and dependent not only on the climate of all other places on Earth, but also on the changes that are taking place in the oceans, within the Earth’s snow and ice cover, and on the land itself. This realisation has also stimulated advances in our understanding of the climate system. These advances are reflected in the development of climatic models. These models, usually couched in terms of mathematical equations expressing the physical laws governing atmospheric behaviour, are beginning to allow us to understand the causes of climate distributions, variations and changes, and to predict the future course of climate.

The recent rapid increase in climatological knowledge has been accompanied by an increase in public awareness of and concern with climate. Most of this stems from ‘global warming’ and the possible consequences, usually regarded as detrimental to society, associated with climate change. The concern extends from this global, long-term phenomenon to many shorter time and smaller area events, whether droughts in the Sahel or Australia, floods in India or the American Midwest, high winds in Britain, an increase in hurricane activity in the eastern United States, or lack of snow-pack in the polar regions. Climatologists are being called upon to address all of these concerns, and increasingly are being expected to provide the appropriate climate predictions.

A major aim of contemporary climatology is clearly to ‘predict’ future climatic conditions. These predictions may involve conditions a few months or years ahead in a specific locality, or those for a time far in the future and covering a major portion of the globe. The present state of development of climatology is such that we are far from providing definitive answers in either of these conditions. Nevertheless, it is clear that significant progress is being made. It is the aim of this book to indicate the present state of our knowledge, point out where further work is possible and suggest areas where further basic research is needed.

1.1 The science of climatology

The science of climatology is founded upon the observation, description and explanation of the physical properties of the Earth’s atmosphere. In general, these physical properties are the familiar climatic elements such as temperature, precipitation, wind, humidity or clouds. The aim of the science is to explain, and eventually predict, these properties. As our understanding and explanation of the observations become more realistic we find that much information and many techniques from other scientific disciplines must be added to the original emphasis on physics (Figure 1.1). This information comes from the traditional allied sciences of chemistry and biology, from the other Earth sciences of geography, geology and oceanography, and, as the linkage between humans and climate becomes more apparent, from the social sciences and in many cases from disciplines such as history, normally regarded as part of the humanities. Nevertheless, throughout this book we shall place emphasis on the climate as a physical system, invoking other disciplines as necessary.

The atmosphere is a body of matter that is constantly in motion. The scales of the motion can range from the molecular, creating heat, to the global, creating the wind systems of the Earth. These motions, on all scales, themselves lead to modifications in the structure and composition of the atmosphere, most notably in the cycling of water and water vapour, which leads to cloud formation and precipitation. All of these motions and their effects are part of climatology and will be considered in detail subsequently. However, as an organising framework for the whole of climatology it is advantageous to use the concept of the energetics of the atmosphere.

Figure 1.1 Factors creating and maintaining the global climate system. Understanding of many of the activities within the various symbolic rectangles must involve many scientific disciplines.

The source of energy for all atmospheric motions is the Sun. Energy from the Sun passes through the atmosphere to the Earth’s surface. During its passage a little energy is absorbed and leads to atmospheric heating, but most of the energy is absorbed at the surface. This surface warms and in turn heats the overlying air, so that the Earth’s surface becomes the main source of heating for the atmosphere. The amount of heating depends greatly on the type of surface as well as the time of day and year. Thus it varies spatially and temporally. The unequal distribution of heat leads directly to the horizontal motions we know as winds, and to the vertical motions which create clouds and precipitation. Eventually the energy that has been received from the Sun and has taken part in the various activities within the atmosphere is returned to space. Hence the climate as we know it can be viewed as a series of energy transformations and exchanges within and between the atmosphere and the underlying surface. These exchanges and transformations act in such a way as to distribute energy over the globe and to maintain an energy balance by returning as much energy to space as is received from the Sun.

The solar energy which drives the climate system changes on a variety of time scales. Consequently the climate also changes. The day-to-day variability, the seasonal shifts, and the differences between one year and the next are all obvious parts of climate, and may have consequences for human activity. Although not as readily detected by human senses, but clearly apparent from various types of historical records, longer-term changes are equally common, and may be equally important from the human perspective. The long-term global rise in temperature over the last 100 years (Figure 1.2), for example, is creating concerns about global warming arising from increasing atmospheric concentrations of greenhouse gases (Table 1.1). Although we think of the atmospheric composition prior to human activity as being unchanging, there has been a slow evolution of the atmosphere during the life of the Earth which has influenced climate.

Figure 1.2 Temperature trends, 1861–1994, expressed as deviations (anomalies) from the 1961–1990 average (‘normal’). These are shown for (a) Northern and (b) Southern Hemispheres separately, and for (c) the whole globe. The same overall trend in both hemispheres, but the different detail, can be seen. In (d) the global anomalies for land and sea are separated. This indicates the slow response of the ocean to atmospheric changes. In (a)–(c) the bars represent individual years, the line a smoothed average of five sucessive years. The bars indicate the great annual variability of climate, even on this global scale, and the smoothed line emphasises the overall warming trend, with the various short-term cooling periods incorporated. (From Nicholls et al., 1996.)

Table 1.1 The composition of the atmosphere

Constituent	Chemical formula	Abundance by volume
Nitrogen	N2	78.08%
Oxygen	O2	20.95%
Argon	Ar	0.93%
Water vapour	H2O	variable (0–4%)
Carbon dioxide^b	CO2	340 ppmv^a
Neon	Ne	18 ppmv
Helium	He	5 ppmv
Krypton	Kr	1 ppmv
Xenon	Xe	0.08 ppmv
Methane^b	CH4	2 ppmv
Hydrogen	H2	0.5 ppmv
Nitrous oxide^b	N2O	0.3 ppmv
Carbon monoxide^b	CO	0.05–0.2 ppmv
Ozone^b	O3	varies (0.02–10 ppmv)
Ammonia	NH3	4 ppbv^a
Nitrogen dioxide	NO2	1 ppbv
Sulphur dioxide	SO2	1 ppbv
Hydrogen sulphide	H2S	0.05 ppbv
Halocarbons^b	CFC, CCl4, etc.	trace

^a ppmv and ppbv are parts per million and parts per billion ...