Irvine, California – Scientists at UC Irvine have found that atmospheric levels of methane have remained relatively stable for the past seven years, following a consistent rise over the previous two decades. The data provides evidence that efforts to reduce emissions of this potent greenhouse gas have had a positive impact, and that further efforts to control methane levels could help mitigate climate change.

Professors F. Sherwood Rowland and Donald R. Blake believe one reason for the slowdown in methane concentration growth may be leak-preventing repairs made to oil and gas lines and storage facilities, which can release methane into the atmosphere. Other reasons may include a slower growth or decrease in methane emissions from coal mining, rice paddies and natural gas production.

Scientists in the Rowland-Blake lab use canisters to collect sea-level air in locations from northern Alaska to southern New Zealand. Then, they measure the amount of methane in each canister and calculate a global average.

From December 1998 to December 2005, the samples showed a near-zero growth of methane, ranging from a 0.2 percent decrease per year to a 0.3 percent gain. From 1978 to 1987, the amount of methane in the global troposphere increased by 11 percent – a more than 1 percent increase each year. In the late 1980s, the growth rate slowed to between 0.3 percent and 0.6 percent per year. It continued to decline into the 1990s, but with a few sharp upward fluctuations, which scientists have linked to non-cyclical events such as the eruption of Mt. Pinatubo in 1991 and the Indonesian and boreal wildfires in 1997 and 1998.

The researchers say there is no reason to believe that methane levels will remain stable in the future, but the fact that levelling off is occurring now indicates that society can do something about global warming. Methane has an atmospheric lifetime of about eight years. Carbon dioxide – the main greenhouse gas that is produced by burning fossil fuels for power generation and transportation – can last a century and has been accumulating steadily in the atmosphere.

Atmospheric levels of methane, the major ingredient in natural gas, have more than doubled since the late 1700s. About two-thirds of methane emissions can be traced to human activities such as fossil-fuel extraction, rice paddies, landfills and cattle. Methane also is produced by termites and wetlands.

Methane has 21 times the impact of carbon dioxide on global warming and accounts for 16 percent of global greenhouse gas emissions when measured in terms of carbon dioxide equivalents (CO2e). Kyoto Protocol targets and ‘carbon credit’ trading systems generally function on the basis of CO2e, so each unit of methane is more valuable economically in terms of carbon credits and environmentally in terms of reducing global warming impacts.

Methane capture and emissions reduction is one area where Canadian companies have developed world-leading expertise and technologies and where they can deliver economically sound environmental solutions both at home and abroad. There are opportunities for the capture and utilization of methane for energy production and to earn carbon credits, such as landfill gas recovery and control of fugitive emissions from the oil and gas industry.