Search

The relationship between human activities and climate change, involving both causes as well as impacts, has become a major issue of concern and interest all over the world. The Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change informs us that the atmospheric concentration of CO2 has increased from 280 ppm in the period 1000-1750 AD to 379 ppm in the year 2005. The terrestrial biospheric exchange had been a cumulative source of about 30 Gt C for the past two centuries but acted as a sink in the 1990s. The concentration of methane in the atmosphere has more than doubled from 700 ppb in the period 1000-1750 AD, to reach a concentration of 1774 ppb in the year 2005. The concentrations of hydrofluorocarbons, perfluorocarbons, SF6 and N2O have also increased. The tropospheric concentration of ozone has increased even though its stratospheric concentration has decreased. The rising emissions and concentrations of all these gases have led to numerous changes in global climate variables. The global mean surface temperature is very likely to have increased by 0.74±0.18°C during the hundred year period 1906-2005. Although the increase is spread out all over the globe, it is greater in the northern hemisphere, and land areas have warmed faster than the oceans. It is very likely that the number of hot days and hot nights has increased and the number of cold days, cold nights and frost has decreased for nearly all land areas. The continental precipitation has increased in the eastern parts of North and South America, northern Europe and central Asia. However, it has decreased in some regions of Africa, southern Asia and the Mediterranean. It is also likely that the area affected by drought has increased since 1970. [ABSTRACT FROM AUTHOR]