NOAA: Global Greenhouse Gas Concentrations Rose in 2005

WASHINGTON, DC, May 1, 2006 (ENS) - Levels of carbon dioxide in the Earth's atmsphere have increased over the past 12 months relative to a 1990 benchmark, according to the Annual Greenhouse Gas Index issed today by the National Oceanic and Atmospheric Administration (NOAA). The greenhouse gas carbon dioxide traps the Sun's heat close to the Earth, causing the global temperature to rise.

The increase in carbon dioxide (CO2) has been somewhat offset by the leveling off of concentrations of another greenhouse gas, methane, the agency said.

Another positive result is the fact that there has also been a decline in two chlorofluorocarbons (CFCs), powerful greenhouse gases that also contribute to causing the Antarctic ozone hole.

Overall, NOAA said, the Annual Greenhouse Gas Index (AGGI) shows a continuing, steady rise in the amount of heat-trapping gases in the atmosphere, although the constant or declining growth rates of methane and CFCs have slightly slowed the overall growth rate of the index.

"We have a better understanding of the dynamics of Earth's climate through our extensive, high quality and sustained observations," said NOAA Administrator Conrad Lautenbacher.

Vice Admiral, U.S. Navy (Ret.) Conrad C. Lautenbacher, Jr., PhD, is under secretary of Commerce for oceans and atmosphere and NOAA administrator. (Photo courtesy NOAA)

While the index has increased in every year since NOAA's global measurements began in 1979, the increase during 2005 was 1.25 percent, which is relatively low, the agency said.

The main source of carbon dioxide in the atmosphere is the burning of fossil fuels - coal, oil and gas - in vehicles, for home heating and in industry.

In the United States, the largest methane emissions come from the decomposition of wastes in landfills, ruminant digestion and manure management associated with domestic livestock, natural gas and oil systems, and coal mining.

The main sources of chlorofluorocarbons are refrigeration systems, both stationary and mobile.

NOAA's Annual Greenhouse Gas Index 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.

NOAA's sampling site at Cape Grim, Tasmania, Australia is operated in cooperation with the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Division of Atmospheric Research. (Photo courtesy NOAA)

Methane concentrations have been holding relatively steady since 1990, the NOAA index shows, because 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.

Most of the increase in radiative forcing measured since 1990 is due to carbon dioxide, 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) to 378.9 ppm.

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.

NOAA's Annual Greenhouse Gas Index, produced by the Global Monitoring Division of the Earth System Research Laboratory in Boulder, Colorado, 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 AGGI will be included in the annual Greenhouse Gas Bulletin issued by the World Meteorological Organization 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.

NOAA monitoring station at Barrow, Alaska above the Arctic Circle (Photo courtesy )

Atmospheric greenhouse gas levels change from year to year depending on natural and human-influenced processes.

The largest annual increase in the Annual Greenhouse Gas Index, 2.8 percent, occurred between 1987 and 1988.

The smallest was .81 percent from 1992 to 1993.

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 sent to Boulder for analysis and comparison with NOAA's world standards for the gases.

Through the emerging Global Earth Observation System of Systems, NOAA is working with its federal partners, 61 countries and the European Commission to develop an integrated global network of information.