The concentration of carbon dioxide in the atmosphere climbed to a record 381 parts per million last year, an increase sure to spark further debate on global warming.
The reading was up 2.6 parts per million, according to preliminary calculations, David J. Hofmann of the Office of Atmospheric Research at the National Oceanic and Atmospheric Administration said Tuesday.
Final calculations from reporting stations around the world won't be available until later in the spring, Hofmann said, but the preliminary numbers are usually quite close.
Carbon dioxide is a major greenhouse gas. Those are chemicals that have been increasing in the atmosphere since the Industrial Revolution, raising fears of altering the planet's climate by trapping heat from the sun.
In Geneva, Switzerland, meanwhile, the World Meteorological Organization issued its own report for 2004, in which Secretary-General Michel Jarraud said, "Global observations coordinated by WMO show that levels of carbon dioxide, the most abundant greenhouse gas in the atmosphere, continue to increase steadily and show no signs of leveling off."
While the total of carbon dioxide in the atmosphere goes up every year the amount of increase varies from year to year, Hofmann said.
The ocean absorbs carbon dioxide at a fairly steady rate, he explained, but some years plants are more active in taking it up as they grow, while in other years they use less. Large forest fires can also release increased amounts of the gas into the air, he said.
"The real question is how long will the earth continue to adjust itself to take up the additional carbon dioxide," he said. "That's one of the major questions."
In addition to carbon dioxide, the 2004 data from WMO calculated that nitrous oxide, which has been rising steadily since 1988, totaled 318.6 parts per billion. Methane has risen the most dramatically over the past two centuries, with the total amount in 2004 at 1,783 parts per billion, but its growth has been slowing, WMO said.
Hans Verolme, director of climate change for the World Wildlife Fund in the United States, welcomed the report as providing an authoritative measurement of the change.
"Unfortunately, it confirms the other data that we've seen from NOAA and NASA, and also it confirms with the trends we've seen in emissions from countries like the United States that still have not taken any real action to reduce carbon pollution," Verolme said.
Leonard Barrie, chief of atmospheric research at WMO, said: "If you have that much more energy being trapped, where does it go? That's the question everybody wants to know. Is it increasing the average surface temperature? Is it increasing storm frequency?"
"Given that the lifetime of carbon dioxide in the atmosphere is 50 to 200 years depending on how you calculate it ... it doesn't take a nuclear scientist to state that we're going to have this problem for a long time," he told reporters at U.N. offices in Geneva. "If we stop now CO2 emissions to the atmosphere, it would take 50 to 100 years before we were starting to see approaches to preindustrial levels."
In September researchers at the Georgia Institute of Technology reported that the number of more powerful hurricanes, category 4 and 5, has increased over the last 20 years, a period when average sea-surface temperature has risen. It's the warm water vapor from the oceans that provides energy for these massive storms.
According to NASA, 2005 had the highest annual average surface temperature worldwide since instrument recordings began in the late 1800s.
Nevertheless, the question of dealing with global climate change has proven a political stumbling block in recent years with the Bush administration rejecting the Kyoto protocol, which seeks to reduce emissions of greenhouse gases.
Scientists worry that overall warming will melt glaciers and the polar ice caps, raising sea levels enough to damage many low-lying islands and cities around the world.
In addition, a warmer climate could lead to changes in weather patterns, agriculture and even allow some diseases to expand into new areas.