Methane May Pack Double the Climate Punch of Earlier Estimates
NEW YORK, New York, July 19, 2005 (ENS) - The impacts of the greenhouse gas methane on climate warming may be double the standard amount attributed to the gas by most scientists today.
Methane, the primary component of natural gas, is said by the U.S. Environmental Protection Agency (EPA) to account for 16 percent of all greenhouse gas emissions resulting from human activities.
New calculations by a NASA scientist show that methane emissions may account for a much greater percentage, up to a third of all climate warming between the 1750s and today.
This idea contrasts with the way greenhouse gases were measured for the major, standard investigations into the state of global warming published in a series of reports from the Intergovernmental Panel on Climate Change (IPCC) Assessment, involving the work of thousands of climate scientists.
The IPCC reports rely on measurements of greenhouse gases as they exist in the atmosphere, after they may have mixed with other gases.
The IPCC states that methane increases in the atmosphere account for only about one sixth of the total effect of well-mixed greenhouse gases on warming.
But Shindell points out that the IPCC findings do not reflect the quantities of gases that were actually emitted.
"The gas molecules undergo chemical changes and once they do, looking at them after they've mixed and changed in the atmosphere doesn't give an accurate picture of their effect," Shindell said.
Emitted from both human and natural sources, these gases are called well mixed greenhouse gases because of their long lifetimes of a decade or more, which allows them to disperse evenly around the atmosphere.
Molecule for molecule, methane is 20 times more potent than carbon dioxide (CO2) as a greenhouse gas, but CO2 is much more abundant than methane and the predicted growth rate is far greater.
Since 1750, methane concentrations in the atmosphere have more than doubled, though the rate of increase has slowed during the 1980s and 1990s, for reasons as yet unknown to scientists, Shindell says.
Combustion of fossil fuels, coal mining, landfills, cattle, and rice paddies are the main human-related sources.
Controlling methane could reap a big bang for the buck, Shindell believes. "If we control methane, which the U.S. is already starting to do, then we are likely to mitigate global warming more than one would have thought, so that's a very positive outcome," he said.
Fourteen countries are already working together to recover methane and use it as a clean energy sources. The Methane to Markets Partnership, launched in Washington, DC on November 16, 2004, includes the United States, the UK, China, Russia, Brazil, India, Italy, Japan, Australia and Nigeria, among others.
Globally, China, Russia, India, the United States, and Brazil are estimated to be responsible for almost half of all methane emissions by human activities. The key methane emission sources for these countries varies. A key source of methane emissions in China is coal production, while Russia emits most of its methane from natural gas and oil systems. Landfills are the largest source of U.S. methane emissions.
These countries are identifying and promoting areas of collaboration on methane recovery and use. They are finding cost-effective opportunities to recover methane emissions for energy production, and potential financing mechanisms to encourage investment.
Previous studies have shown that new rice harvesting techniques can reduce methane emissions and increase yields. Draining a flooded rice field at specific times during the crop cycle can reduce methane emissions by up to half without decreasing rice yields.
Now, Shindell says his work shows that, "Control of methane emissions turns out to be a more powerful lever to control global warming than would be anticipated."
He points to another bonus of this perspective, that in order to manage greenhouse gases, policy decisions must focus on cutting emissions, because that is where humans have some control. When policy makers know what the emissions actually are, they will have more control, Shindell believes.
Shindell finds there are advantages to measuring emissions of greenhouse gases and isolating their impacts, as opposed to analyzing them after they have mixed in the atmosphere.
"The amount of methane in the atmosphere is affected by pollutants that change methane's chemistry, and it doesn't reflect the effects of methane on other greenhouse gases," said Shindell, "so it's not directly related to emissions, which are what we set policies for."
Shindell was named by "Scientific American" magazine as a Research Leader for the 2004 Scientific American 50 — the magazine’s annual list recognizing outstanding acts of leadership in science and technology from the past year.
His methane measurements study was recently published in the journal "Geophysical Research Letters."
To find out more, visit Dr. Shindell's web page at: http://www.giss.nasa.gov/~dshindel/