What are the causes of global warming?

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What are the causes of global warming?

1- Human activities

• Human activities are considered one of the main causes of global warming. Several human activities increase the emission of certain greenhouse gases into the atmosphere. When fossil fuels such as oils, natural gas, and coal, in addition to wood, wood products, and solid waste are burned they emit Carbon Dioxide. During both industrial and agricultural activities and the combustion of solid waste and fossil fuels nitrous oxide is emitted. The actual percentage of Carbon dioxide recorded is and increase by 31% since 1750 and about ¾ of this increase is from deforestation and the burning of fossil fuels.

www.encyclomedia.com/global_warming.html

Science Links Global Warming to Human Activity

In February 2007, a report by the Intergovernmental Panel on Climate Change (IPCC), representing the work of 2,500 scientists from more than 130 countries, stated that human activity "very likely" has been the primary cause of global warming since 1950. (In science, nothing is ever claimed to be "certain" or absolute, which leaves open the possibility of further research and discovery, but the term “very likely” indicates more than 90 percent certainty and is considered virtual confirmation.) The IPCC report also said that human activity has been a major contributor to climate change since the start of the Industrial in the mid-1700s.

http://environment.about.com/od/faqglobalwarming/f/greengaseshuman.htm

2- The greenhouse effect

• When sunlight reaches Earth's surface some is absorbed and warms the earth and most of the rest is radiated back to the atmosphere at a longer wavelength than the sun light. Some of these longer wavelengths are absorbed by greenhouse gases in the atmosphere before they are lost to space. The absorption of this longwave radiant energy warms the atmosphere. These greenhouse gases act like a mirror and reflect back to the Earth some of the heat energy which would otherwise be lost to space. The reflecting back of heat energy by the atmosphere is called the "greenhouse effect".

• The major natural greenhouse gases are water vapor, which causes about 36-70% of the greenhouse effect on Earth (not including clouds); carbon dioxide CO2, which causes 9-26%; methane, which causes 4-9%, and ozone, which causes 3-7%. It is not possible to state that a certain gas causes a certain percentage of the greenhouse effect, because the influences of the various gases are not additive. Other greenhouse gases include, but are not limited to, nitrous oxide, sulfur hexafluoride, hydrofluorocarbons, perfluorocarbons and chlorofluorocarbons.