Major greenhouse gases in the air are accumulating faster than in the past, despite efforts to curtail their growth.
Carbon dioxide concentration in the air increased by 2.4 parts per million last year, the National Oceanic and Atmospheric Administration reported Wednesday, and methane concentrations also rose rapidly.
Concern has grown in recent years about these gases, with most atmospheric scientists concerned that the increasing accumulation is causing the earth's temperature to rise, potentially disrupting climate and changing patterns of rainfall, drought and other storms.
The Intergovernmental Panel on Climate Change has worked to detail the scientific bases of this problem and the Kyoto agreement sought to encourage countries to take steps to reduce their greenhouse emissions.
Some countries, particularly in Europe, have taken steps to reduce emissions.
But carbon dioxide emissions, primarily from burning fossil fuels such as coal, oil and gas, have continued to increase.
Since 2000, annual increases of two parts per million or more have been common, compared with 1.5 ppm per year in the 1980s and less than one ppm per year during the 1960s, NOAA's Earth System Research Laboratory said.
Global concentration of carbon dioxide is now nearly 385 parts per million. Preindustrial carbon dioxide levels hovered around 280 ppm until 1850. Human activities pushed those levels up to 380 ppm by early 2006.
Rapidly growing industrialization in Asia and rising wetland emissions in the Arctic and tropics are the most likely causes of the recent methane increase, said Ed Dlugokencky from NOAA's Earth System Research Laboratory.
Methane in the atmosphere rose by 27 million tons last year after nearly a decade with little or no increase, he said.
Methane is 25 times more potent as a greenhouse gas than carbon dioxide, but there's far less of it in the atmosphere, partly because it slowly breaks down into carbon dioxide and water.
When related climate affects are taken into account, methane's overall climate impact is nearly half that of carbon dioxide.