Climate change is a newcomer to the international political and environmental agenda, having emerged as a major policy issue only in the late 1980s and thereafter. It has emerged since the 19th century that CO2 in the atmosphere is a ‘greenhouse gas’, that is, its presence in the atmosphere helps to retain the incoming heat energy from the sun, thereby increasing the earth’s surface temperature. Of course, CO2 is only one of several such greenhouse gases in the atmosphere. Others include methane, nitrous oxide and water vapour. However, CO2 is the most important greenhouse gas that is being affected by human activities. CO2 is generated by a multitude of processes. Since the Industrial Revolution, when our usage of fossil fuels increased dramatically, the contribution of CO2 from human activities has grown large enough to constitute a significant perturbation of the natural carbon cycle. The concentration of CO2 in the Earth’s atmosphere was about 280 parts per million by volume (ppmv) in 1750, before the Industrial Revolution began. By 1994 it was 358 ppmv and rising by about 1.5 ppnw per year. If emissions continue at the 1994 rate, the concentration will be around 500 ppmv, nearly double the pre-industrial level, by the end of the 21st century.