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Monday, May 01, 2006

NOAA Reports Continued Increase in Atmospheric Greenhouse Gases

The National Oceanic and Atmospheric Administration (NOAA) issued the latest global Annual Greenhouse Gas Index (AGGI) today, its benchmark measurement of gases in the atmosphere that affect the Earth’s climate. This year's AGGI shows a continuing, steady rise in the amount of heat-trapping gases in the atmosphere overall.

That steady increase reflects an increase in carbon dioxide (CO2) and nitrous oxide (N2O) but a leveling off of methane (CH4), and a decline in two chlorofluorocarbons (CFCs), gases that contribute to the cause of the Antarctic ozone hole [see figures below].

According to NOAA, the AGGI is referenced to a baseline value of 1.00 for the greenhouse gas levels that were present in the atmosphere in 1990. The value of the AGGI for 2005 is 1.215. This reflects a continuing upward trend in the accumulation of greenhouse gases, as well as the change in the amount of radiative forcing.

Radiative forcing indicates the balance between radiation coming into the atmosphere and radiation going out, NOAA explains. Positive radiative forcing tends on average to warm the surface of the Earth, and negative forcing tends on average to cool the surface. Radiative forcing, as measured by the index, is calculated from the atmospheric concentration of each contributing gas and the per-molecule climate forcing of each gas [i.e. the global warming potential (GWP) of each gas].

The constant or declining growth rates of methane and CFCs have slightly slowed the overall growth rate of the AGGI, NOAA reports. Methane concentrations have been holding relatively steady since 1990. This is mostly attributed to an equilibrium that has been reached between sources of emission of the gas, its duration in the atmosphere and areas where it is taken out of the atmosphere. Another positive result is the fact that CFCs are continuing to decline. Along with creating the ozone hole over the Antarctic, CFCs are also very powerful greenhouse gases [HFC-23, for example, has a GWP of 260 times that of CO2!].

According to NOAA, most of the increase in radiative forcing measured since 1990 is due to CO2, which now accounts for approximately 62 percent of the radiative forcing by all long-lived greenhouse gases. During 2005, global CO2 increased from an average of 376.8 parts per million (ppm) in 2004 to 378.9 ppm, NOAA reports. This increase of 2.1 ppm means that for every one million air molecules there were slightly more than two new CO2 molecules in the atmosphere. The pre-industrial CO2 level was approximately 278 ppm.

[Figure: Radiative forcing of all the long-lived greenhouse gases, relative to 1750, and the NOAA Annual Greenhouse Gas Index (AGGI) on the right axis, which is indexed to 1 on January 1, 1990.]

NOAA's AGGI, produced by the Global Monitoring Division of the Earth System Research Laboratory in Boulder, Colo., is a recently developed index that provides an easily understood and scientifically unambiguous point of comparison for tracking annual changes in levels of atmospheric greenhouse gases. The NOAA AGGI will be included in the annual Greenhouse Gas Bulletin issued by the World Meteorological Organization (WMO) in November.

The AGGI is based on the analyses of atmospheric levels of all the major and minor long-lived greenhouse gases, and factors in the relative strengths of each gas in its ability to trap heat. The gases include carbon dioxide, methane, nitrous oxide, CFCs and the current replacements for CFCs, and have been measured since 1979 by NOAA's global sampling network.

Atmospheric greenhouse gas levels change from year to year depending on natural and human-influenced processes. According to NOAA, the largest annual increase in the AGGI, 2.8 percent, occurred between 1987 and 1988 while the smallest was .81 percent from 1992 to 1993. The index has increased in every year since NOAA's global measurements began in 1979. However, according to this year's AGGI, the increase during 2005 was 1.25 percent, which is relatively low.

NOAA's network of five global baseline observatories and about 100 global cooperative sampling sites extends from the high Arctic to the South Pole. Samples also are taken at five-degree latitude intervals from three oceanic ship routes. A Baltic ferry line collects samples as it makes its daily crossing. All samples are then sent to Boulder for analysis and comparison with NOAA's world standards for the gases.

NOAA, an agency of the U.S. Department of Commerce, is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation's coastal and marine resources.

Through the emerging Global Earth Observation System of Systems (GEOSS), NOAA is working with its federal partners, 61 countries and the European Commission to develop a global network that is as integrated as the planet it observes, predicts and protects.


  • NOAA Annual Greenhouse Gas Index (AGGI)

  • NOAA Global Monitoring Division

  • NOAA Earth System Research Laboratory

  • [A hat tip to Green Car Congress]

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