Global warming is the increase in average temperature of the air near the earth's surface and oceans since the mid-20th Century and its projected continuation. The scientific consensus is that global warming is under way and, above all the result of human activity. This statement is recognized by the national academies of sciences of all major industrial countries and rejected by all scientific institutions, national or international prestige.
During the 20th Century, the temperature of the earth's surface 0.74 ± 0.18 ° C (1.33 ± 0.32 ° F). Most of the observed warming since the middle of the twentieth century, caused 20 of increasing concentrations of greenhouse gases from human activities like burning fossil fuels and deforestation.
With regard to future warming, the 2007 report of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) projections of climate models used to evaluate the six scenarios of emissions of greenhouse gases. After the most likely scenario of the actual global emissions of greenhouse gases, would the temperature of the earth's surface by 6.4 ° C further1.1 (2.0 to 11.5 ° F) increase for the year 2100, and the upper limit of this range is not included heating of the possible release of some reactions of the carbon cycle. For the year 2010 confirmed the recent observations A1FI emissions scenario "business as usual" case and that "the most pessimistic IPCC trajectories scene or, even worse." For example, some of the carbon cycle feedbacks throws in the A1FI scenario, the best estimate of a temperature increase of 4 ° C in late 2070 and 5 degrees Celsius by 2090, with a potential of between 3-7 ° C, and even the conservative estimate, because it seems that the comments of permafrost, which could be extreme.