Important Greenhouse Gas Stopped Growing


UC Irvine Professors F. Sherwood Rowland and Donald R. Blake, in conjunction with researchers Isobel J. Simpson and Simone Meinardi, have discovered that the amount of methane in the atmosphere has stabilized and shown little increase over the past seven years, despite steadily increasing levels of the greenhouse gas for at least two decades beforehand.
Supported by NASA and the Gary Comer Abrupt Climate Change Fellowship, the researchers’ results convey that methane may no longer pose as large threat to global warming and, instead, may be controlled. Their results also affirm that the increase of methane is directly correlated to the increase of ethane, which is a natural gas released from burning fires. This discovery supports the idea that methane is generated when biomass burns and, as a result, increased levels of methane result from increased numbers of large fires.
Researchers propose that leakage-preventing adjustments to oil and gas lines and storage venues may account for the stable levels of methane in the environment. In addition, the slowdown of coal mines, rice paddies and natural gas production may also be linked to the decrease in methane levels.
‘If one really tightens emissions, the amount of methane in the atmosphere 10 years from now could be less than it is today,’ said Rowland in a press release dated Nov. 20. ‘We will gain some ground on global warming if methane is not as large a contributor in the future as it has been in the past century.’
Rowland currently works as a Donald Bren research professor of chemistry and earth system science and was a corecipient of the 1995 Nobel Prize in Chemistry. He found that chlorofluorocarbons, which are found in products such as coolants and aerosol sprays, were destroying the ozone layer, which protects the Earth by filtering the sun’s harmful rays.
Since the Industrial Revolution in the late 1700s, methane emissions have more than doubled. Aggregations such as fossil-fuel burning, rice paddies, landfills, termites, wetlands and cattle account for approximately two-thirds of the methane in the environment.
To obtain their results, scientists collected sea-level air from northern Alaska to southern New Zealand and measured the amount of methane from each area to calculate a global average of methane.
The air samples showed little growth from December 1998 to December 2005, whereas levels of methane from 1978 to 1987 increased by one percent each year. The growth rate decreased beginning in the late 1980s and continued to decline in the 1990s. The only fluctuations that occurred during this period of overall decline were due to unexpected events, such as the eruption of Mount Pinatubo in 1991.
The Rowland-Blake lab also measured ethane and perchloroethylene, a chlorinated solvent that is usually involved with the dry-cleaning process. Ethane and methane were directly linked, whereas perchloroethylene demonstrated a different fluctuating trend from methane.
The study indicated that methane levels may not remain stable in the future, although society may now be able to control the amount of methane in the environment and thus control global warming. Methane can remain in the atmosphere for approximately eight years, in contrast to carbon dioxide, which also comes from the burning of fossil fuels and can last up to a century. While levels of methane may be decreasing, carbon dioxide levels have been steadily increasing.
‘If carbon dioxide levels were the same today as they were in 2000, the global warming discussion would leave the front page,’ Rowland said. ‘But to stabilize this greenhouse gas, we would have to cut way back on emissions. Methane is not as significant a greenhouse gas as carbon dioxide, but its effects are important. The world needs to work hard to reduce emissions of all greenhouse gases.’
The publication ‘Geophysical Research Letters’ will feature the full study in its Nov. 23 online edition.

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