The science of global warming

There is strong scientific evidence that the average temperature of the earth's surface is rising as a result of the increased concentration of carbon dioxide and other greenhouse gases in the atmosphere owing to human activities, especially the burning of fossil fuels, coal, oil, and gas. This global warming will lead to substantial changes of climate, many of which will impact human communities in deleterious ways. In terms of the likely global pattern of climate change over the twenty-first century, in the absence of any mitigating action the global average temperature is likely to rise by between about 1-5 and 5-5degreesC and sea level by about half a metre (range 0(.)1-0(.)9 m). The hydrological cycle is likely to be more intense (leading in some places to more frequent and more intense floods and droughts) and the rate of climate change is likely to be substantially greater than the earth has experienced over at least the last ten thousand years. It is particularly to this rapid rate of change that it will be difficult for many ecosystems and for humans to adapt. Action has been taken by the world's scientists through the Intergovernmental Panel on Climate Change to assess as thoroughly as possible knowledge regarding the basic science and the impacts, including an assessment of the uncertainties. The world's governments have also taken action in setting up the Framework Convention on Climate Change (FCCC) at the Earth Summit in 1992 and at subsequent meetings of the parties to that convention, especially that at Kyoto in 1997. In order to mitigate climate change the FCCC in its article 2 has set the objective of stabilisation of the concentration of greenhouse gases in the atmosphere at a level and on a timescale consistent with the needs both of the environment and of sustainable development. Such stabilisation will eventually demand severe cuts in global emissions, for instance of carbon dioxide, to levels well below today's by the second half of the twenty-first century. To achieve the required reductions in the emissions of carbon dioxide, three possibilities are available, to sequester carbon dioxide resulting from the burning of fossil fuels rather than releasing it to the atmosphere, to become much more efficient in the generation and use of energy, and to provide for energy supply from non-fossiI fuel sources. This article will summarise the science of climate change including the evidence for it and will describe the main impacts, the actions taken so far, and the further actions that are likely to be necessary to mitigate climate change.