WASHINGTON - The effect of greenhouse gases on the Earth's atmosphere has increased 20 percent since 1990, a new government index says.

The Annual Greenhouse Gas Index was released Tuesday by the Climate Monitoring and Diagnostics Laboratory in Boulder, Colo.

Greenhouse gases such as carbon dioxide accumulate in the atmosphere as a result of industrial and other processes. They can help trap solar heat, somewhat like a greenhouse, resulting in a gradual warming of the Earth's atmosphere.

The Earth's average temperature increased about 1 degree Fahrenheit during the 20th century. The Intergovernmental Panel on Climate Change warns that continuing increases could have serious effects on crops, glaciers, the spread of disease, rising sea levels and other changes.

In its new analysis the laboratory, a branch of the National Oceanic and Atmospheric Administration, compares the amounts of carbon dioxide, methane, nitrous oxide and chlorofluorocarbons in the air. Those gases have been sampled for many years.

The index was set to a reading of 1 as of 1990 and the lab said it is currently 1.20, indicating an increase of 20 percent.

"The AGGI will serve as a gauge of success or failure of future efforts to curb carbon dioxide and other greenhouse gas increases in the atmosphere both by natural and human-engineered processes," said David Hofmann, CMDL director.

The index is expected to be updated each April.

"This index provides us with a valuable benchmark for tracking the composition of the atmosphere as we seek to better understand the dynamics of Earth's climate," said NOAA Administrator Conrad C. Lautenbacher, Jr.

In the current reading, for every million air molecules there are about 375 carbon dioxide molecules, two are methane and less than one is a nitrous oxide molecule. The CFC's make up less than one molecule in a billion in the atmosphere but play a role in regulating Earth's climate and are a key factor in the depletion of the protective ozone layer, NOAA researchers say.

The gases produce an effect known as radiative forcing. It is a shift in the balance between solar radiation coming into the atmosphere and Earth's radiation going out. 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.

The lab said most of the increase measured since 1990 is due to carbon dioxide, which now accounts for about 62 percent of the radiative forcing by all long-lived greenhouse gases.

NOAA said the 1990 baseline was chosen because greenhouse gas emissions targeted by the international Kyoto Protocol also are indexed to 1990.

___

On the Net:

NOAA Climate Monitoring and Diagnostics Lab: http://www.cmdl.noaa.gov

Commentary: