From the end of the last glacial episode about 7 to 10Ka up to the mid-eighteenth century, the levels of greenhouse gases in the atmosphere remained fairly constant. Since the Industrial Revolution, concentrations of most of the major greenhouse gases have increased, to a greater or lesser extent. The effect of this has been to increase the greenhouse radiative forcing of the climate. With more greenhouse gases in the atmosphere, more outgoing terrestrial radiation is trapped in the lower atmosphere, leading, presumably, to increases in surface temperature.
The debate as to whether this anthropogenic pollution of the atmosphere has increased global surface temperatures is ongoing. The following sections of this chapter (sections 6.4 to 6.8) offer a review of the evidence for anthropogenic global warming. I will begin with a discussion of the sources and sinks of the various greenhouse gases (section 6.4), before investigating how changes in their concentrations over the last 200 years have affected the radiative forcing of the global climate (section 6.5). In section 6.7 observed climate changes are reviewed, whilst section 6.8 discusses the question of detection [of anthropogenic warming].