What is global warming?Global warming is the rise in the averagetemperature of Earths atmosphere and oceans.Since the early 20th century, Earths average surfacetemperature has increased by about 0.8 °C withabout two-thirds of the increase occurring since1980. Warming of the climate system is definite.Scientists are more than certain that it is primarilycaused by increasing concentrations of greenhousegases produced by human activities such as theburning of fossil fuels and deforestation. Thesefindings are recognized by the national scienceacademies of all major industrialized nations. Itsprojected to continue.
Greenhouse Effect• The greenhouse effect is a process by which thermal radiation from a Earth’s surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since a part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases.• Some greenhouse gases are: Water vapour, Carbon Dioxide, Methane, Nitrous Oxide, Ozone, Chloroflorocarbons, Argon, etc
Details of some GHGs• Carbon Dioxide (CO2) – Source: Fossil fuel burning, deforestation Anthropogenic increase: 30% Average atmospheric residence time: 500 years Methane (CH4) – Source: Rice cultivation, cattle & sheep ranching, decay from landfills, mining Anthropogenic increase: 145% Average atmospheric residence time: 7-10 years Nitrous oxide (N2O) – Source: Industry and agriculture (fertilizers) Anthropogenic increase: 15% Average atmospheric residence time: 140-190 years