The greenhouse effect and global warming - Global Environmental Issues - page 145

Table 7.1 Sources of greenhouse gas emissions

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 CO 2 ,
and the destruction of natural vegetation has
prevented the environment from restoring the
balance. Levels of other greenhouse gases,
including CH 4 , N 2 O 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).