Carbon dioxide (CO2) is released into the atmosphere by the burning of wood, coal, oil and gas. Increases in the amount of CO2 in the atmosphere are of special interest to scientists because carbon dioxide is a significant heat-trapping greenhouse gas.

As measured in air samples collected from more than 60 sites in the NOAA Global Cooperative Observing Network, the amount of CO2 in the atmosphere increased by nearly 5 parts per million (ppm) between 2001 and 2003. The increase in 2002 was 2.43 ppm; the increase in 2003 was 2.30 ppm.

In other words, more than two additional carbon-dioxide molecules were added to each million molecules of air each year during that period. The annual increase was higher than the long-term average annual CO2 increase of approximately 1.5 ppm.

Included in the global average carbon dioxide measurements are those from the NOAA Mauna Loa Observatory in Hawaii where the CO2 record is the world's longest continuous observations of atmospheric carbon-dioxide levels, having begun in 1958.

The increased CO2 levels interested scientists who questioned whether some unknown mechanism might be causing the atmosphere to retain higher levels of CO2.

However, according to David Hofmann, director of the NOAA Climate Monitoring and Diagnostics Laboratory in Boulder, Colo., the rate of carbon-dioxide increase returned to the long-term average level of about 1.5 ppm per year in 2004, indicating that the temporary fluctuation was probably due to changes in the natural processes that remove CO2 from the atmosphere.

Global combustion of fossil fuels and other materials places almost 7 billion tons of carbon, in the form of CO2, into the atmosphere each year.

On average, Earth's oceans, trees, plants and soils absorb about one-half of this carbon. The balance remains in the air and is responsible for the annual increase.

Most of the variability in the year-to-year CO2 uptake is related to natural processes, including droughts and fires as well as such factors as global temperatures, rainfall amounts and volcanic eruptions.

Understanding these processes is key to forecasting annual CO2 increases, thus providing important information for future CO2 management.

NOAA's Carbon Cycle Research Program, which includes surface-, ocean- and space-based measurements of CO2 and other important atmospheric gases, is aimed at developing a comprehensive picture of how CO2 is stored and released.

The carbon-cycle studies are a part of NOAA's Climate Program, an integral part of the U.S. Climate Change Science Program.

"Reducing scientific uncertainties of carbon sources and sinks is a priority for the Climate Change Science Program, as carbon dioxide is the single largest forcing agent of climate change," said James R. Mahoney, NOAA deputy administrator and CCSP director.

NOAA scientists have been tracking CO2 levels around the world for more than 25 years. The oldest record comes from the Mauna Loa Observatory, which is located atop a Hawaiian volcano.

There, Charles Keeling began CO2 measurements in 1958. Following NOAA's formation in 1970, measurements continued at Mauna Loa and began at other places around the world. There are now more than 60 monitoring sites worldwide.

Mahoney adds, "The measurement capabilities established at NOAA's Mauna Loa and other sites around the world demonstrates the importance of observational networks as a contribution to understanding the complexities of the carbon cycle."

Each year since global measurements of CO2 began, the amount of carbon dioxide in the atmosphere has increased.

Scientific measurements of levels of CO2 contained in cylinders of ice, called ice cores, indicate that the pre-industrial carbon dioxide level was 278 ppm. That level did not vary more than 7 ppm during the 800 years between 1000 and 1800 A.D.

Atmospheric CO2 levels have increased from about 315 ppm in 1958 to 378 ppm at the end of 2004, which means human activities have increased the concentration of atmospheric CO2 by 100 ppm or 36 percent.

NOAA 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. NOAA is part of the U.S. Department of Commerce.

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