It is the existence of trace gases in the atmosphere that act like the glass in a greenhouse. The trace gases serve to trap the heat energy from the Sun close to Earth. Most greenhouse gases occur naturally. Greenhouse gases are cycled through the global biogeochemical system. It is the greenhouse gases added by human activity that are trapping too much heat today and causing the atmosphere to overheat. There are several different types of greenhouse gases, some existing in greater quantities than others. They include water vapor, CO2, methane, nitrous oxide, and halocarbons. Greenhouse gases capture 70 to 85 percent of the energy in upgoing thermal radiation emitted from the Earth's surface.
Water vapor is the most common greenhouse gas—it accounts for roughly 65 percent of the natural greenhouse effect. Water exists in many places on the Earth's surface—lakes, rivers, and oceans. When water heats up, it evaporates into vapor and rises from the Earth's surface into the atmosphere. It forms clouds and can act as a insulating blanket to help keep the Earth warm, or it can reflect and scatter incoming sunlight. This is why cloudy nights are warmer than clear nights. As water vapor condenses and cools, it then comes back to the Earth as snow or rain and continues on its way through the water cycle.
CO2 is generated from several sources. The second most prevalent greenhouse gas, it comprises about 25 percent of the natural greenhouse effect. Humans and animals exhale CO2; vegetation releases CO2 when it dies and decomposes; burning trees in a forest fire or burning during deforestation release it; burning fossil fuels (such as exhaust from cars and industrial processes) are all common sources of CO2.
Methane is a colorless, odorless, flammable gas formed when plants decay in an environment of very little air. It is the third-most common greenhouse gas and is created when organic matter decomposes without the presence of oxygen—a process called anaerobic decomposition. One of the most common sources is from "ruminants"—grazing animals that have multiple stomachs in which to digest their food. These include cattle, sheep, goats, camels, bison, and musk ox. In their digestive system, their large fore-stomach hosts tiny microbes that break down their food. This process creates methane gas, which is released as flatulence. Livestock also emit methane when they belch. In fact, in one day a single cow can emit one-half pound of methane into the air. Each day 1.3 billion cattle burp methane several times per minute. Humans also produce methane.
Methane is also a by-product of natural gas and decomposing organic matter, such as food and vegetation. Also present in wetlands, it is commonly referred to as "swamp gas." Since 1750, methane has doubled its concentration in the atmosphere, and it is projected to double again by 2050. According to Nick Hopwood and Jordan Cohen at the University of Michigan, every year 350 to 500 million tons of methane are added to the atmosphere through various activities, such as the raising of livestock, coal mining, drilling for oil and natural gas, garbage sitting in landfills, and rice cultivation. Rice cultivation is a huge global business. In the past 50 years, rice farmland has doubled in area. Rice is a major food staple; it currently feeds one-third of the world's population. Because rice is grown in waterlogged soils, like swamps, they release methane as a by-product.
Nitrous oxide (N2O), another greenhouse gas, is released from manure and chemical fertilizers that are nitrogen-based. As the fertilizer breaks down, N2O is released into the atmosphere. Nitrous oxide is also contained in soil by bacteria. When farmers plow the soil and disturb the surface layer, N2O is released into the atmosphere. It is also released from catalytic converters in cars and also from the ocean. According to Hopwood and Cohen, nitrous oxide has risen more than 15 percent since 1750. Each year 7-13 million tons (6-12 million metric tons) is added to the atmosphere principally through the use of nitrogen-based fertilizers, the disposal of human and animal waste in sewage treatment plants, automobile exhaust, and other sources that have not been identified yet. The use of nitrogen-based fertilizers has doubled in the last 15 years. Although good for the productivity of crops, they break down in the soil and release N2O into the atmosphere.
Halocarbons include the fluorocarbons, methylhalides, carbon tetrachloride (CCl4), carbon tetrafluoride (CF4), and halons. They are all considered to be powerful greenhouse gases because they strongly absorb terrestrial infrared radiation and stay in the atmosphere for many decades.
Fluorocarbons are a group of synthetic organic compounds that contain fluorine and carbon. A common compound is chlorofluoro-carbon (CFC). This class contains chlorine atoms and have been used in industry as refrigerants, cleaning solvents, and propellants in spray cans. These fluorocarbons are harmful to the atmosphere, however, because they deplete the ozone layer; their use has been banned in most areas of the world, including the United States.
Hydrofluorocarbons (HFCs) contain fluorine and do not damage the ozone layer. Fluorocarbon polymers are chemically inert and electrically insulating. They are used in place of CFCs because they do not harm or break down ozone molecules, but they do trap heat in the atmosphere. HFCs are used in air conditioners and refrigerators. The best way to keep HFCs out of the atmosphere is to recycle the coolant from the equipment they are used in.
Fluorocarbons have several practical uses. They are used in anesthetics in surgery, as coolants in refrigerators, as industrial solvents, as lubricants, water repellents, stain repellents, and chemical reagents. They are used to manufacture fishing line and are contained in products such as Gore-Tex and Teflon.
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Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.