Annual Greenhouse Gas Index (AGGI) Indicates Sharp Rise in Carbon Dioxide and Methane in 2007April 23, 2008
Last year alone global levels of atmospheric carbon dioxide, the primary driver of global climate change, increased by 0.6 percent, or 19 billion tons. Additionally methane rose by 27 million tons after nearly a decade with little or no increase. NOAA scientists released these and other preliminary findings today as part of an annual update to the agency's greenhouse gas index, which tracks data from 60 sites around the world.
The burning of coal, oil, and gas, known as fossil fuels, is the primary source of increasing carbon dioxide emissions. Earth's oceans, vegetation, and soils soak up half of these emissions. The rest stays in the air for centuries or longer. Twenty percent of the 2007 fossil fuel emissions of carbon dioxide are expected to remain in the atmosphere for thousands of years, according to the latest scientific assessment by the International Panel on Climate Change.
Viewed another way, last year's carbon dioxide increase means 2.4 molecules of the gas were added to every million molecules of air, boosting the global concentration to nearly 385 parts per million (ppm). Pre-industrial carbon dioxide levels hovered around 280 ppm until 1850. Human activities pushed those levels up to 380 ppm by early 2006.
The rate of increase in carbon dioxide concentrations accelerated over recent decades along with fossil fuel emissions. Since 2000, annual increases of two ppm 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.
Methane Levels on the Rise
Methane levels rose last year for the first time since 1998. Methane is 25 times more potent as a greenhouse gas than carbon dioxide, but there's far less of it in the atmosphere -- about 1,800 parts per billion. When related climate affects are taken into account, methane's overall climate impact is nearly half that of carbon dioxide.
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 scientist Ed Dlugokencky from NOAA's Earth System Research Laboratory.
"We're on the lookout for the first sign of a methane release from thawing Arctic permafrost," said Dlugokencky. "It's too soon to tell whether last year's spike in emissions includes the start of such a trend."
Permafrost, or permanently frozen ground, contains vast stores of carbon. Scientists are concerned that as the Arctic continues to warm and permafrost thaws, carbon could seep into the atmosphere in the form of methane, possibly fueling a cycle of carbon release and temperature rise.
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