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Contact: Barbara McGehan
News Releases 2003
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One of the atmosphere’s most potent greenhouse gases, methane, may now have leveled off, according to a study by researchers from the Commerce Department’s National Oceanic and Atmospheric Administration (NOAA), and National Institute for Space Research in the Netherlands. Scientists aren’t sure yet if this “leveling off” is just a temporary pause in two centuries of increase or a new state of equilibrium.
The study appears in the Nov. 18 issue of Geophysical Research Letters. Lead author Ed Dlugokencky of NOAA’s Climate Monitoring and Diagnostics Laboratory (CMDL) in Boulder, Colo., said the study is based on air samples from a globally distributed network of over 43 monitoring sites. The air samples show that global methane has been constant over the past four years, suggesting that methane emissions may be approximately equal to losses.
“Our observation that atmospheric
methane has been constant for four years is good news for climate,
but our limited understanding of what caused this result makes it
impossible to predict whether or not methane levels will continue
to remain constant,” Dlugokencky said.
“This reported decrease in methane emission rates may have moved the global methane budget toward a steady state, although the annual variability in methane emission rates is too large to say so with certainty,” Dlugokencky said. Scientists have been projecting that methane levels would continue to increase in the atmosphere at a significant rate, so this new equilibrium was not expected.
Methane is a trace gas that has more than doubled in the atmosphere since pre-industrial times, due mainly to human activities. After water vapor and carbon dioxide, it is the most important greenhouse gas and accounts for approximately 20 percent of the human-influenced greenhouse gas warming potential.
While methane is emitted to the atmosphere by some natural sources, such as wetlands, more than 70 percent of total emissions are due to human activities including fossil fuel production and use, intestinal gas from livestock and farm animals, and cultivation of rice paddies. Since many methane sources are the result of human activities, increased industrialization in developing countries and stepped up global food demand could result in increased emissions in the future.
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