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Politics : Foreign Affairs Discussion Group

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To: Nadine Carroll who wrote (250354)	12/2/2007 2:49:30 PM
From: c.hinton	Read Replies (2) of 281500

look at methane and the amount of time it lingers please. Methane in the Earth's atmosphere is an important greenhouse gas with a global warming potential of 25 over a 100 year period. This means that a 1 tonne methane emission will have 25 times the impact on temperature of a 1 tonne carbon dioxide emission during the following 100 years. Methane has a large effect for a brief period (about 10 years), whereas carbon dioxide has a small effect for a long period (over 100 years). Because of this difference in effect and time period, the global warming potential of methane over a 20 year time period is 72. The methane concentration has increased by about 150% since 1750 and it accounts for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases.[8] The average mole concentration of methane at the Earth's surface in 1998 was 1,745 ppb.[9] Its concentration is higher in the northern hemisphere as most sources (both natural and human) are larger. The concentrations vary seasonally with a minimum in the late summer. Methane is created near the surface, and it is carried into the stratosphere by rising air in the tropics. Uncontrolled build-up of methane in Earth's atmosphere is naturally checked—although human influence can upset this natural regulation—by methane's reaction with a molecule known as the hydroxyl radical, a hydrogen-oxygen molecule formed when single oxygen atoms react with water vapor. Early in the Earth's history—about 3.5 billion years ago—there was 1,000 times as much methane in the atmosphere as there is now. The earliest methane was released into the atmosphere by volcanic activity. During this time, Earth's earliest life appeared. These first, ancient bacteria added to the methane concentration by converting hydrogen and carbon dioxide into methane and water. Oxygen did not become a major part of the atmosphere until photosynthetic organisms evolved later in Earth's history. With no oxygen, methane stayed in the atmosphere longer and at higher concentrations than it does today.

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