Is global warming attributable to human activities?
For the past 420 000 years global atmospheric carbon dioxide has only varied between about 180 and 280 parts-per-million (ppm), and stayed steady at about 280 ppm from 1 000 to 250 years ago. However, since the beginning of the Industrial Revolution, some 250 years ago, the concentrations of greenhouse gases in the atmosphere have increased dramatically. Human activities, such as burning fossil fuels (coal, oil and gas), land clearing and agricultural practices have: • increased carbon dioxide by more than a third • increased nitrous oxide levels by about 17 per cent • methane concentrations have more than doubled. The observed changes in climate, especially temperature increases since about 1970, cannot be explained by natural causes such as solar activity. Scientists use computer models to simulate past and future climate variations. Reconstructions of climate data for the past 1 000 years indicate that this recent warming is unusual and is unlikely to have resulted from natural caus
