The greenhouse effect and global warming

The succession of exceptional years with record high temperatures, which characterized the 1980s, helped to generate widespread popular interest in global warming and its many ramifications. The decade included six of the warmest years in the past century, and the trend continued into the 1990s, with 1991 the second warmest year on record. All of this fuelled speculation—especially among the media—that the earth's temperature had begun an inexorable rise, and the idea was further reinforced by the results of scientific studies which indicated that global mean temperatures had risen by about

0.5°C since the beginning of the century (see Figure 7.1).

Periods of rising temperature are not unknown in the earth's past. The most significant of these was the so-called Climatic Optimum, which occurred some 5,000-7,000 years ago and was associated with a level of warming that has not been matched since. If the current global warming continues, however, the record temperatures of the earlier period will easily be surpassed. Temperatures reached during a later warm spell in the early Middle Ages may well have been equalled already. More recently, the 1930s

Figure 7.1 Measured globally-averaged (i.e. land and ocean) surface air temperatures for this century

Figure 7.1 Measured globally-averaged (i.e. land and ocean) surface air temperatures for this century

Source: After Jones and Henderson-Sellers (1990)
Table 7.1 Sources of greenhouse gas emissions




Percentage of global total


Fossil fuel combustion Natural gas leakage Industrial activities Biomass burning

C02, CH4/ N20, 03

54 3



C02/ CH4/ N20



Rice production (paddies) Animal husbandry (ruminants) Fertilizer use


Waste management

Sanitary landfill waste disposal Incineration Biomass decay

C02/ CH4/ N20, 03/ CFC



Cement production CFC production/use


C02, N20, CFC

11.5 8.5

Source: After Green and Salt (1992)

Source: After Green and Salt (1992)

provided some of the highest temperatures since records began, although that decade has been relegated to second place by events in the 1980s. Such warm spells have been accepted as part of the natural variability of the earth/ atmosphere system in the past, but the current warming is viewed in a different light. It appears to be the first global warming to be created by human activity.

The basic cause is seen as the enhancement of the greenhouse effect, brought on by rising levels of anthropogenically-produced greenhouse gases (see Table 7.1). It is now generally accepted that the concentrations of greenhouse gases in the atmosphere have been increasing since the latter part of the nineteenth century. The increased use of fossil fuels has released large amounts of CO2, and the destruction of natural vegetation has prevented the environment from restoring the balance. Levels of other greenhouse gases, including CH4, N2O and CFCs have also been rising. Since all of these gases have the ability to retain terrestrial radiation in the atmosphere, the net result should be a gradual increase in global temperatures. The link between recent warming and the enhancement of the greenhouse effect seems obvious. Most of the media, and many of those involved in the investigation and analysis of global climate change, seem to have accepted the relationship as a fait accompli. There are only a few dissenting voices, expressing misgivings about the nature of the evidence and the rapidity with which it has been embraced. A survey of environmental scientists involved in the study of the earth's changing climate, conducted in the spring of 1989, revealed that many still had doubts about the extent of the warming. More than 60 per cent of those questioned indicated that they were not completely confident that the current warming was beyond the range of normal natural variations in global temperatures (Slade 1990).

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Survival Basics

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