Methane
Methane is second only to carbon dioxide in its impact as a greenhouse gas. It comes from landfills, livestock, natural gas systems, wetlands, and natural gas stores within the earth.
Methane is more commonly known as swamp gas. This is the second most abundant greenhouse gas and it is 21 times more efficient at warming than CO2. CO2 is much more abundant in the atmosphere and remains in the atmosphere for a much longer period of time than methane and therefore has a larger overall warming effect in the atmosphere than methane does. Methane is produced anthropogenically by landfills, ruminant livestock, biomass burning and natural gas systems. Some natural sources are wetlands and termites. Methane is the largest component of natural gas, which is used as a fuel source once the contaminants are removed.
The atmospheric lifespan of a molecule of methane is estimated to be around 12 years. From 650,000 years ago until the industrial revolution, the concentration of CH4 never rose above .00000073% or 730ppb. However, the current CH4 concentration, as of 2009, is around .000001774% or 1774ppb. In the past fifteen years the concentration has not increased much, but scientists are hesitant to celebrate. Some theories state that there are variations in output from wetlands and biomass burning, or there are more removal processes than previously thought.
Methane Up Sharply; Ozone Impact Studied
A sharp increase in methane gas in the atmosphere since 1978 will probably make the earth warmer and may worsen seasonal losses of protective ozone over Antarctica, scientists say.
But the 11 percent increase in methane in the last decade may also slow depletion of the ozone shield over the rest of the planet, said F. Sherwood Rowland and Donald R. Blake, chemists at the University of California at Irvine.
Their study, financed by the National Aeronautics and Space Administration, was published Friday in the journal Science.
Methane is the major component of natural gas, but about 80 percent of atmospheric methane comes from decomposition in rice paddies, swamps and the intestines of cows, with some contribution from wood digestion in termites, Mr. Rowland said.
Humans are responsible for increased methane levels because they are raising more cows, growing more rice and chopping down tropical forests, which provides food for more termites, said atmospheric scientist Pat Zimmerman of the National Center for Atmospheric Research in Boulder, Colo.
Mr. Blake and Mr. Rowland collected air samples regularly from January 1978 to September 1987 at up to 60 locations around the Pacific to measure methane levels. Their study indicates the rate of increase in methane gas slowed slightly in the last five years. The Greenhouse Effect
Researchers generally agree that by trapping solar heat like glass in a greenhouse, methane, carbon dioxide and other pollutants are likely to warm the earth's lower atmosphere by a few degrees in the next half century.
They fear this greenhouse effect may cause crop-threatening droughts and partly melt polar ice caps, raising sea levels.
Ozone is an air pollutant at low altitudes, but in the stratosphere it shields the earth from harmful ultraviolet radiation. Scientists say reduction of the ozone layer will cause more skin cancers and ecological damage.
In 1974, Mr. Rowland and a chemist, Mario Molina, first warned that the ozone layer was threatened by man-made chlorine compounds called chlorofluorocarbons, or CFC's, which are used as refrigeration coolants, aerosol propellants and for making plastic foams. The United States banned spray-can CFC's in 1978. A global treaty aims to reduce global output of CFC's and other ozone-destroying chemicals.
Mounting evidence indicates CFC's are responsible for the worldwide loss of about 1 percent of the earth's ozone shield and drastic thinning of the ozone layer above Antarctica for a few months starting every September. Ice Clouds Over Antarctica
Mr. Blake and Mr. Rowland said methane increases might worsen the Antarctic ozone hole by aiding formation of ice clouds above Antarctica. Studies by Molina and others suggest the clouds enhance chemical reactions that allow chlorine from CFC's to break down ozone.
As methane rises into the polar stratosphere, it breaks down and releases hydrogen, which combines with a chemical called hydroxyl to form water, which in turn freezes into clouds, Mr. Blake explained.
Outside Antarctica, wind and higher temperatures prevent formation of stratospheric clouds. Instead, by attacking chlorine from CFC's, methane may reduce the amount of chlorine available to destroy ozone, Mr. Blake said.
The 11 percent methane increase ''will make the ozone hole over Antarctica more severe,'' said Mr. Molina, who is at the National Aeronautics and Space Administration's Jet Propulsion Laboratory in Pasadena. ''It will probably make the ozone depletion in the rest of the world less severe,'' he said.
Mr. Rowland and Mr. Blake also said that because increasing atmospheric methane reduces the amount of hydroxyl present, it may reduce the atmosphere's ability to cleanse itself of pollutants. Hydroxyl reacts with many pollutants and removes them from the atmosphere.
Methane and Carbon Dioxide. Methane is five time more effective than Carbon dioxide. The major sources of Methane are melting permafrost and cows flatulence. Methane builds up in old permanently frozen ice aka permafrost, and the united states is trying to find a better diet for cows to produce less gas. Carbon Dioxide is getting stronger from deforestation and car emissions.
0 komentar:
Post a Comment