In Focus: Greenhouse Gas Increases Accelerating
More detailed measurements encouraged
The National Oceanic and Atmospheric Administration announced last week that increases in two major greenhouse gases accelerated in 2007.
Carbon dioxide (CO2), the primary contributor to global warming, increased by 0.6%, which represents an addition to the atmosphere of 19 billion tons, or 2.4 parts per million (ppm). This brings the total atmospheric concentration to about 385 ppm, an increase of 37.5% from the pre-industrial level of 280 ppm prior to 1850. The annual increases of 2 ppm -- common since 2000 -- are up from 1.5 ppm annually in the 1980s and less than 1 ppm per year in the 1960s.
Although CO2 is well mixed in the atmosphere, knowledge of regional distribution of sources and sinks of the gas requires more detailed measurements than the average values reported by NOAA.
In a commentary article in the April 25 edition of Science, a magazine of the American Association for the Advancement of Science, University of Colorado and NOAA researchers suggest that the global monitoring network should be made 10 times larger -- by increasing the number of measuring sites from about 100 to 1,000 -- to better track progress in emission reductions.
NOAA also announced that methane, which is 25 times stronger than CO2 as a greenhouse gas, increased for the first year since 1998. Fortunately for climate effects, methane density in the atmosphere is much less than for CO2, about 1.8 ppm.
One of the biggest wildcards in climate prediction, however, involves the potential feedback effects from increasing methane. Very large amounts of methane are currently trapped in the form of clathrate, an ice-like structure that embeds methane molecules within a solid water molecule lattice. Release of this methane from arctic permafrost or ocean sediments could lead to accelerated greenhouse warming. Under a theory called the "Clathrate Gun Hypothesis," destabilization of the clathrate reservoir could lead to drastic climate consequences.
A 2006 article, "Shallow Seabed Methane Gas Could Pose Coastal Hazard," in the American Geophysical Union's Eos publication explored the possible effects on climate change and sea level rise in the next century from methane "generated in shallow seabed sediments on continental margins, especially in rapidly deposited muddy sediments with high organic matter content." An article last year by Swedish, Russian and German researchers, "Nearshore Arctic Subsea Permafrost in Transition" raises the issue of whether "degradation of subsea permafrost and the consequent destabilization of gas hydrates could significantly if not dramatically increase the flux of methane, a potent greenhouse gas, to the atmosphere."
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