Methane (CH4) is a significant greenhouse gas, and is a natural part of the atmosphere. Ice core records going back many thousand years show that methane levels, like CO2 levels, rise and fall with global temperature. Methane (also called 'swamp gas') is formed by bacterial action in wet locations where oxygen is in short supply. These include swamps, garbage dumps, rice paddies, and the digestive systems of cattle, termites, and even man. Because increased temperature accelerates bacterial activity, a small temperature rise can result in large increases in methane production in soils, swamps, and wetlands. Some of the observed 1.0 percent annual increase in CH4 is probably due to the current greenhouse heating of the earth. This is the most likely reason why CH4 levels fluctuated with temperature during glacial and interglacial times.
Methane is also produced by many of man's industrial activities. Since CH4 is a principal ingredient in natural gas, any leaks in gas transmission pipes will add menthane to the air. Methane also leaks out of the ground when coal is mined. These industrial sources are estimated to account for perhaps 20% of global emissions. The average methane molecule spends about 10 years in the troposphere (below 40,000 feet) and is eventually destroyed by photochemical reactions with hydroxyl radicals (OH). Hydroxyl radicals, however, are in short supply in the air presently because of increasing levels of carbon monoxide (CO). Thus, even though CO pollution does not directly cause greenhouse warming, it contributes to increased methane levels, which do.
As can be seen from the above discussion, methane levels will be difficult to control. Some CH4 sources involve natural mechanisms, many others are created through necessary food production. Methods to reduce the rate of methane build-up involve building more fuel-efficient cars, reducing wasteful industrial combustion that generates CO, reduced use of coal, and measures to control natural gas leakage. Scientists at the University of California, Irvine just released a study showing methane levels to be very high in most cities in Eastern Europe - due to old, leaky gas pipes. Apparently after years of Communist management, the natural gas distribution system has fallen into such disrepair that an estimated 10% of the gas leaks into the air, never reaching its destination! Repairing/replacing gas lines in these countries is a relative simple way to reduce CH4 levels. Leaks in the US gas distribution system are estimated to be at about 2%.
Reducing CO2 and other greenhouse gases will also reduce methane releases due to the natural temperature feedback mechanism. ***
