Methane
Methane is a colorless, odorless gas with a wide distribution in nature. Anaerobic bacterial from the decomposition of plant and animal matter, such as occurs under water, produces marsh gas, which is also methane. The importance of methane in the greenhouse effect is its warming effect. Even though it occurs in lower concentrations than carbon dioxide, it produces 21 times as much warming per molecule as carbon dioxide. Methane accounts for 20% of the enhanced greenhouse effect.
Methane is combustible, and mixtures of about 5 to 15 percent in air are explosive. It is not toxic when inhaled, but it can produce suffocation by reducing the concentration of oxygen inhaled.
The abundance of methane in the earth's atmosphere in 1998 was 1745 parts per billion (ppb), up from 700 ppb in 1750. By 2008, however, global methane levels, which had stayed mostly flat since 1998, had risen to 1,800 ppb and by 2010, methane levels, at least in the arctic, were measured at 1850 ppb, a level scientists described as being higher than at any time in the previous 400,000 years, while noting that historically, methane concentrations in the world's atmosphere have ranged between 300 and 400 ppb in cool periods and 600 to 700 ppb in warm periods.
Methane can trap about 20 times the heat of carbon dioxide. In the same time period, carbon dioxide increased from 278 to 365 parts per million. The radiative forcing effect due to this increase in methane abundance is about one-third of that of the carbon dioxide increase. In addition, there is a large, but unknown, amount of methane in methane clathrates in the ocean floors. The Earth's crust contains huge amounts of methane. Large amounts of methane are produced anaerobically by methanogenesis. Other sources include mud volcanoes, which are connected with deep geological faults, landfill and livestock (primarily ruminants) from enteric fermentation.
Since the Industrial Revolution, the level of Methane in the atmosphere has increased by two and a half times.
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[edit] Industrial uses
In the form of natural gas methane serve as common fabric, plastic, anti-freeze and fertilizer ingredient. Industrial natural gas consumers include companies that make pulp and paper. Food processors, petroleum refineries and companies that work with stone, clay and glass, use the energy it releases. Methane-based combustion helps businesses dry, dehumidify, melt and sanitize their products. The use of methane natural gas in commercial settings also resembles home uses.
[edit] Power generation
Methane in natural gas form can produce electricity. Turbines and natural gas fuel cells can produce enough electrical energy to power a home.
Methane-rich landfill gas is created as organic solid waste gradually breaks down through the process of anaerobic decomposition. The biogas consists of approximately 50% Methane, 49% Carbon Dioxide and 1% trace gases, which, if allowed to emit into the atmosphere, are significant contributors to global warming. Converting methane to energy reduces the emissions from the landfill and reduces reliance on fossil fuels.
[edit] The natural methane cycle
Methane is generated naturally by bacteria that break down organic matter, it is found in the guts of termites and other animals and in natural gas deposits. It can remain in the atmosphere for 11-12 years - less time than most other greenhouse gases.
Methane is removed from the atmosphere through a natural process to form water. Currently little is known about the volume of methane that passes in and out of the atmosphere, but it is thought that this is in balance.
[edit] The impact of human activities
An increase in livestock farming and rice growing has led to an increase in atmospheric methane. Other sources are the extraction of fossil fuels, landfill sites and the burning of biomass.
[edit] Methane and Climate change
Human-influenced sources of methane include landfills, natural gas and petroleum systems, agricultural activities, coal mining, stationary and mobile combustion, wastewater treatment, and certain industrial process.
A United Nations report has identified of rapidly growing of livestock industry as the greatest threat to the climate, forests and wildlife. Livestock are responsible for 18 per cent of the greenhouse gases that cause global warming, more than cars, planes and all other forms of transport combined. Burning of fossil fuels to produce fertilizer to grow feed, to produce meat and to transport it - and clearing vegetation for grazing - produces 9 per cent of all emissions of carbon dioxide. And their wind and manure emit more than one third of emissions of another, methane, which warms the world 20 times faster than carbon dioxide.
The leading greenhouse gases include carbon dioxide, methane, nitrous oxide, and halocarbons. These gases are called ‘well mixed’ greenhouse gases because of their long lifetimes of a decade or more, which allows them to disperse evenly around the atmosphere. They are emitted from both man-made and natural sources. Ozone in the lower atmosphere, called tropospheric ozone, a major component of polluted air or smog that is damaging to human and ecosystem health, also has greenhouse warming effects.
