Greenhouse Gas
Posted by admin on 25 Apr 2007 | Tagged as: Global Warming
What are Greenhouse Gases?
Greenhouse gases are the gases present in the atmosphere which reduce the loss of heat into space and therefore contribute to global temperatures through the greenhouse effect. Greenhouse gases are essential to maintaining the temperature of The Earth; without them the planet would be so cold as to be uninhabitable. However, an excess of greenhouse gases can raise the temperature of a planet to lethal levels, as on Venus where the 96.5% carbon dioxide (CO2) atmosphere results in surface temperatures of about 467 °C (872 °F). On earth, the term greenhouse gas is applied to, in order of relative abundance: water vapour, carbon dioxide, methane, nitrous oxide, ozone and CFCs. Greenhouse gases are produced by many natural and industrial processes, which currently result in CO2 levels of 380 ppmv in the atmosphere. Based on ice-core samples and records (see graphs) current levels of CO2 are approximately 100 ppmv higher than during immediately pre-industrial times, when direct human influence was negligible.
The average global air temperature near the Earth’s surface increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the hundred years ending in 2005. The Intergovernmental Panel on Climate Change (IPCC) concludes "most of the observed increase in globally averaged temperatures since the mid-twentieth century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations" via the greenhouse effect. Natural phenomena such as solar variation combined with volcanoes probably had a small warming effect from pre-industrial times to 1950 and a small cooling effect from 1950 onward. These basic conclusions have been endorsed by at least thirty scientific societies and academies of science, including all of the national academies of science of the major industrialized countries. While individual scientists have voiced disagreement with some findings of the IPCC, the overwhelming majority of scientists working on climate change agree with the IPCC’s main conclusions.
Climate model projections summarized by the IPCC indicate that average global surface temperature will likely rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the twenty-first century. The range of values results from the use of differing scenarios of future greenhouse gas emissions as well as models with differing climate sensitivity. Although most studies focus on the period up to 2100, warming and sea level rise are expected to continue for more than a thousand years even if greenhouse gas levels are stabilized. The delay in reaching equilibrium is a result of the large heat capacity of the oceans.