CIRES Study Detects Large Methane Emissions over Amazon

Earth’s largest tropical rainforest is emitting much larger volumes of methane into the atmosphere than was previously estimated, according to a field study led by John B. Miller at the Cooperative Institute for Research in Environmental Sciences (CIRES) and NOAA Earth System Research Laboratory. According to the study, which was published in Geophysical Research Letters (May 25, 2007), Amazonian emissions contribute an average of 34 parts per billion of methane in excess of background sites in the Atlantic Ocean. This concentration of methane is roughly equivalent to 20% of the entire north-south concentration difference of methane in the atmosphere.

Background: While recent satellite observations have suggested that the Amazon emits large amounts of methane, the CIRES study is the first to directly measure these emissions. Between 2000 and 2003, Miller’s team took samples from a vertical column of air -- stretching from the surface to 13,000 feet altitude -- at two locations in the central Amazon. They compared these to air samples taken at remote Atlantic islands, which represent background air entering the Amazon basin.

Significance: Methane is about 25 times more potent a greenhouse gas than carbon dioxide. While the total global abundance of methane is well documented, much less is understood about the relative importance of individual methane sources, especially sources in the tropics, where relatively few measurements have been made. The contribution of vegetation to atmospheric methane concentrations has been especially challenging to assess, as there is yet no way to distinguish between direct-plant and wetland emissions. The CIRES study brings scientists one step closer to understanding the relative strength of individual sources of this important greenhouse gas. This study research supports NOAA Mission Goal 2 - Understand Climate Variability and Change to Enhance Society's Ability to Plan and Respond.