In terms of sheer weight, carbon dioxide accounts for around 85 percent of America’s greenhouse gas emissions, which amounted to 7.074 billion metric tons in 2004; methane accounts for just 8 percent of that frightening total. On top of that, carbon dioxide is often spotlighted because it’s so closely linked to the appalling fossil-fuel dependence decried by treehuggers and politicians alike: Ninety-four percent of the US human caused CO₂ emissions are due to fossil-fuel combustion. Human related (anthropogenic) methane emissions, come from the decomposition of garbage in landfills and belching ruminants (cows, sheep etc).

Methane is 21 times more effective at preventing infrared radiation from escaping the planet than carbon dioxide. So, although methane emissions may be relatively piddling, they’re definitely a cause for concern. It does break down faster however.

Then we have nitrous oxide, only about 40 percent of these emissions are anthropogenic, with agricultural fertilizers being the main source. However the gas is 310 times more effective at preventing infrared radiation from escaping the planet than carbon dioxide (310 GWP) and it has an atmospheric lifetime of 120 years—10 times longer than that of methane.

There are small amounts of others such as sulphur hexafluoride. Chiefly used for a range of esoteric applications—such as preventing molten magnesium from oxidizing and for etching semiconductor wafers—SF₆ has a GWP of 23,900, making it the most brutally effective greenhouse gas known to man. And sulphur hexafluoride’s its atmospheric lifetime is a depressing 3,200 years.

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This entry was posted on Thursday, December 6th, 2007 at 11:08 pm and is filed under Global Warming, Climate Change & Energy. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.