The politicization of global warming

The work of Revelle and Suess (1957) really gave scientific credence to modern-day worries about global warming. In a review of the growing awareness of global warming Kellogg (1987) reports on the early non-scientific interest in the topic. In 1963 a USA non-governmental organization (NGO), the Conservation Foundation, organized a meeting on global warming. It concluded that a doubling of carbon dioxide in the atmosphere would lead to an increase of global temperatures of 3.8 C (Conservation...

The Little Ice

It is difficult to give an exact period for the Little Ice Age as it varied from place to place. Lamb (1982) defined it as the period between 1420 and 1850 with 1550 to 1800 being the maximum. The 1500s were the peak of the Renaissance and the Reformation. There was a commensurate increase in documentary evidence and, by the 1700s, systematic instrumental observations (Bradley and Jones, 1992). In Europe between 1500 and 1800 it is believed the mean winter temperature was 1.3 C lower than for...

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Figure 4.2 Minima and maxima in solar activity Source Eddy (1977) geomagnetic variations. Stuiver and Quay (1980) found major increases in carbon-14 production during 1282-1342 Wolf Minimum, 1450-1534 Sporer Minimum and 1645-1715 Maunder Minimum. These correspond well to the minimum of sunspots and auroral activity. By using carbon-14 activity and the sunspot number Eddy (1977) was able to identify far more solar minima in the historical past (see Fig. 4.2). Beryllium-10 is also produced by...

The model evidence for global warming

The previous chapter showed that there is a lot of observational evidence which suggests that the amount of greenhouse gases in the atmosphere and the global average surface temperature are rising. By now though you should realize that linking the two is far from straightforward. It is almost an impossible task to prove, before any significant climate change, that it is human pollution that is responsible for both these upward trends. So apart from the physics and the observations, scientists...

Energy

Energy is very important to the climate system. It is energy which drives the system and is constantly being exchanged from one component to the next. Energy is defined as the ability to do work and in physics work occurs when an object moves over some distance due to a force acting along the line of the movement. Sears, Zemansky and Young (1978) put forward the following example of work. Supposing someone asked you to move a heavy box for them. If you were to push it along a level floor you...

Processes affecting electromagnetic radiation

Electromagnetic radiation is everywhere, coming from the Sun in the form of heat and light, and from all the objects around us. What happens to that electromagnetic radiation when it reaches an object That will depend on the wavelength of the incident light, the angle at which it strikes the surface and the nature of the surface, to name some of the most important. There are two important processes that can occur called absorption and scattering. These will be discussed after a brief review of...

The Geochemical model

This model is based on the carbonate-silicate cycle which forms part of the carbon cycle as discussed in Chapter 2 (Walker et al., 1981). Rain removes carbon dioxide from the atmosphere as dilute carbonic acid. At the surface this acid combines with the silicate materials which converts the carbon dioxide into bicarbonate. These bicarbonates are then dissolved in water and carried to the oceans. In the oceans the carbonates are incorporated into the shells of sea creatures. Eventually these...

Early history

Between 5000 bc and 3000 bc the global average temperature was probably some 1 to 3 C warmer than it is now. From 4000 to 2440 bc it is possible that the African Monsoon occurred as far north as the Sahara, implying greater vegetation and a more moist regime in this area. Evidence of this comes from rock paintings which depict agriculture and animals such as hippopotamus in an area which now sees very little rainfall. During this period the Early Kingdom cultures in Egypt flourished next to the...

Climate and weather

The Earth continually receives energy from the Sun. If there was not something to balance this incoming energy then the Earth would always be heating up. The Earth, however, emits energy out into space, often called terrestrial energy, so it loses heat. One might expect that the outgoing energy at each location on the globe would have to exactly match that coming in, in order to maintain a balance, however, observations show that this is not the case. The latitudinal distribution of solar...

The climate system

Usually it is the value the various variables take at some particular time that is of concern this is called the system state. The number of variables to be considered is determined by the length of time chosen to study the system. Over short time-scales some variables may hardly alter and so they can effectively be considered as constant. For longer time-scales, however, more variables will have to be studied as more will change. This is particularly true of the climate system. As a system...

Equilibrium and stability

If the solar output was to suddenly double, the various components of the climate system would all start to respond in line with their response times. Eventually a new energy balance would be reached and the climate would be in equilibrium. Chapter 1 introduced equation (1.9) to calculate the temperature at the top of the atmosphere the energy balance equation. That equation was solved to find T by using present-day values of SQ and a. If the solar output doubled you would obviously get a new...

Global warming potential

The concept of a radiative forcing was introduced in Chapter 2. This is much easier to assess than the climatic response because of the feedbacks within the climate system. Radiative forcing can provide a simple measure of how important each greenhouse gas is relative to the others although the concept of radiative forcing has limitations when considering the full implications of climate change. Therefore there has been great emphasis in the various IPCC reports on determining the radiative...

References

Adkins, J.F., Boyle, E.A., Keigwin, L. and Cortijo, E. 1997 Variability of the North Atlantic thermohaline circulation during the last interglacial period. Nature 390, 154-6. Arnell, N. 1999 The effects of climate change on hydrological regimes in Europe a continental perspective. Global Environmental Change 9, 5-23. Bengtsson, L., Roeckner, E. and Stendel, M. 1999 Why is global warming proceeding much slower than expected Journal of Geophysical Research-Atmospheres 104, 3865-76. Bretherton,...

The Earths radiation and energy budget

The Earth atmosphere system derives its energy in the form of radiation from the Sun. A change in the output of the Sun either in intensity or spectral characteristics would affect the energy available to the Earth-atmosphere system and would affect the climate. The total amount of radiation per unit area incident on a surface perpendicular to the Earth at the top of the atmosphere when the Earth is at a mean distance from the Sun is called the solar constant So . Its present-day value is...

Halocarbons

Methyl chloride CH3Cl is one of the few halocarbons that has a natural source, most are synthetic. It is produced by the oceans and by biomass Figure 5.3 A simplified diagram of the nitrogen cycle Figure 5.3 A simplified diagram of the nitrogen cycle burning but it does not appear to be increasing Watson et al., 1990 . The halocarbons that have received most attention of late are chlorofluorocarbons CFCs . This group of chemicals are entirely synthetic, developed commercially in the early...

The lithosphere

The lithosphere is the surface crust of the Earth, the mountains, rocks and ocean basins. While it does interact with the overlying atmosphere, by transfers of mass and energy, its very long response time means that except for geological time-scales, the lithosphere can be regarded as unchanging. On geological time-scales continental drift, uplift and subsidence may all play a role in the modulating the climate. Interactions feedbacks and sensitivity The sub-systems of the climate are not...

Absorption of longwave radiation

Chapter 2 showed how absorption is spectrally selective. A molecule of a substance only absorbs certain wavelengths. If there is enough of that substance it will absorb all the radiation at that wavelength. In the case of the atmosphere such a gas would make the atmosphere opaque in that wavelength. There have been objections to global warming on the grounds that the carbon dioxide 15 m absorption band is already saturated and so therefore increasing carbon dioxide will lead to no change in the...

Global warming

The Earth's atmosphere acts just like a blanket. On a cold winter's night you feel nice and warm but put your hand outside on top of the blanket and it's a lot colder. The Earth's surface remains far warmer than the top of the atmosphere because the atmosphere traps the heat. Water, particularly water vapour, carbon dioxide and other trace gases in the atmosphere are all very effective absorbers of infra-red radiation. They absorb the long-wave radiation coming up from the surface of the Earth....

Introduction

The previous chapter introduced some of the ways in which the physical sciences are used to inform policy decisions and this raised some interesting ethical issues. It would be impossible for this book to address all these issues and many of the them pertain to wider problems such as the relationship between the north and south the developed and developing world. This book is looking at the science of climate change and this chapter is devoted to the way science has informed the wider issues...

Case Studies

There are various events, usually in military history, that illustrate how short-term climatic events, really meteorological phenomena, have influenced the course of history. In the late eighteenth century France hoped to attack England by inciting rebellion in Ireland. The French fleet was to land at Bantry Bay in December 1796. While initially fog protected the French fleet from the English it also prevented efficient communication amongst the fleet. There then followed a period of unsettled...

The components

Anything that changes the Earth's energy balance will result in the climate system readjusting itself, attempting to compensate for the change and coming to a new balance point. The natural changes which occur in this energy balance are usually called forcings. As these forcings cause a change in the radiation balance, essentially a change in the net radiation, they are referred to as radiative forcings and are measured in the same units as radiation Win . These forcings occur on a variety of...

The geological climate record

It was the geological evidence of liquid water on Earth that presented the Faint Sun Paradox. How can one reconstruct the past geological climate for the geological time-scale, see Figure 3.3 There are no direct measurements of the temperature and the climate is deduced from data that reflect the natural conditions of the past. As these data are not direct measurements of the climate they are called proxy data. Oxygen-18 isotope analysis, sediment formation, rock weathering, formation of water...

Geological climate change

There are many slow long-term changes, apart from the change in solar luminosity, that affect the climate of the Earth. Prior to 3 x 10 years ago the Earth was mostly covered in water see Fig. 3.4 . Around 250 million years ago there existed one large supercontinent called Pangaea. This broke up about 180 million years ago into two continents called Gonwanaland and Laurasia. Gowanaland is believed to have been composed of South America, Africa, Australia, India and Antarctica. Laurasia was made...