General issues on Environmental ecology : Global warming

Global warming refers to the rising average temperature of Earth's atmosphere and oceans, which began to increase in the late 19th century and is projected to continue rising. Since the early 20th century, Earth's average surface temperature has increased by about 0.8 °C, with about two thirds of the increase occurring since 1980.Most of it is caused by increasing concentrations of greenhouse gases produced by human activities such as deforestation and burning fossil fuels. Recently World Meteorological Organization Secretary-General Michel Jarraud warned that the consequences of global warming could be permanent. "The world is warming because of human activities and this is resulting in far-reaching and potentially irreversible impact on our Earth, atmosphere and oceans," he said.


Climate models
Climate models are systems of differential equations based on the basic laws of physics, fluid motion, and chemistry. To “run” a model, scientists divide the planet into a 3-dimensional grid, apply the basic equations, and evaluate the results. Atmospheric models calculate winds, heat transfer, radiation, relative humidity, and surface hydrology within each grid and evaluate interactions with neighboring points. They are used for a variety of purposes from study of the dynamics of the climate system to projections of future climate. The most talked-about use of climate models in recent years has been to project temperature changes resulting from increases in atmospheric concentrations of greenhouse gases.
Climate model projections are summarized  by the Intergovernmental Panel on Climate Change (IPCC). They indicate that during the 21st century the global surface temperature is likely to rise a further 1.1 to 2.9 °C for their lowest emissions scenario and 2.4 to 6.4 °C for their highest. If global mean temperature increases to 4 °C (7.2 °F) above preindustrial levels, the limits for human adaptation are likely to be exceeded in many parts of the world, while the limits for adaptation for natural systems would largely be exceeded throughout the world. Hence, the ecosystem services upon which human livelihoods depend would not be preserved.

Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change (IPCC) is a scientific intergovernmental body established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP). Later it was endorsed by the United Nations General Assembly through Resolution 43/53. Its mission is to provide comprehensive scientific assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and socio-economic consequences, and possible options for adapting to these consequences or mitigating the effects. It is chaired by Rajendra K. Pachauri.

Thousands of scientists and other experts contribute (on a voluntary basis, without payment from the IPCC) to writing and reviewing reports, which are reviewed by representatives from all the governments, with summaries for policy makers being subject to line-by-line approval by all participating governments.

The IPCC does not carry out its own original research, nor does it do the work of monitoring climate or related phenomena itself. A main activity of the IPCC is publishing special reports on topics relevant to the implementation of the United Nations Framework Convention on Climate Change (UNFCCC), an international treaty that acknowledges the possibility of harmful climate change. Implementation of the UNFCCC led eventually to the Kyoto Protocol. The IPCC has published four comprehensive assessment reports reviewing the latest climate science, as well as a number of special reports on particular topics.  fourth assessment report (AR4) was released in 2007 and a fifth is due to be issued in 2014.

Permafrost
Permafrost or cryotic soil is soil at or below the freezing point of water 0 °C (32 °F) for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of the ground material. Most permafrost is located in high latitudes (i.e. land close to the North and South poles). Permafrost accounts for 0.022% of total water and exists in 24% of exposed land in the Northern Hemisphere.

Temperature variation in Earth

Temperature changes vary over the globe. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade). Ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because the ocean loses more heat by evaporation. The Northern Hemisphere warms faster than the Southern Hemisphere because it has more land and because it has extensive areas of seasonal snow and sea-ice cover subject to ice-albedo feedback. Although more greenhouse gases are emitted in the Northern than Southern Hemisphere this does not contribute to the difference in warming because the major greenhouse gases persist long enough to mix between hemispheres.

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