Geophys. Res. Lett. 34, L10809 (2007)

Credit: JOHN B. MILLER, NOAA

The eastern Amazon River basin is emitting more methane than climate models take into account. An air sample analysis has now confirmed satellite data showing that the Amazon basin produces large amounts of the potent greenhouse gas. This suggests that scientists have underestimated the tropics as a methane source.

John B. Miller of the US National Oceanic and Atmospheric Administration and colleagues analysed samples taken by aircraft at a range of altitudes over two areas in eastern Amazonia from 2000 to 2003. They found that the region emits an average of 27 mg of methane per square metre per day. The Amazon contributes on average 34 parts per billion of methane to the air flowing over Brazil from the Atlantic, and can contribute bursts as high as 200 parts per billion.

The researchers say more tropics methane measurements are needed to better understand global trends. Human methane sources are on the rise, but this has been offset by an unusual decrease in methane emissions from wetlands. If wetland emissions recover or other natural sources increase, global atmospheric methane levels could rise above what is already a dramatic increase over pre-industrial levels.