World's major greenhouse gases emitted into the atmosphere has increased rapidly over the level of 1990, U.S. National Oceanic and Atmospheric Administration (NOAA) reported on Monday.

Releasing the greenhouse gas index of the year 2005, the agency said there is a "continuing, steady rise" in the emission of carbon dioxide (CO2) and nitrous oxide (N2O), two heat-trapping gases linked with global warming.

The index is referenced to a baseline value of 1.00 for the atmospheric greenhouse gas levels in 1990. The value for year is 1. 215, the NOAA said.

"This reflects a continuing upward trend in the accumulation of greenhouse gases," the agency said in a statement. The index' rise means the radiative forcing, which tends to warm earth surface, is growing, it said.

Among the greenhouse gases globally monitored by the agency, the concentration of carbon dioxide has increased by about 30 parts per million (ppm) in 25 years, while the concentration of nitrous oxide has grown by 12 parts per billion (ppb).

The carbon dioxide is the major gas blamed for global warming, accounting for approximately 62 percent of the radiative forcing by all long-lived greenhouse gases, the agency said.

During 2005, global carbon dioxide concentration has reached 378.9 ppm, while the pre-industrial CO2 level was approximately 278 ppm.

However, the concentration of another greenhouse gas, methane, has leveled off in recent years, according to the agency. And another good result is that the emission of two chlorofluorocarbons (CFCs), gases linked with the Antarctic ozone hole, is in decline.

The index 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, according to the NOAA.

The monitored gases include carbon dioxide, methane, nitrous oxide, CFCs and the current replacements for CFCs.

Source: Xinhua