Weighing Up Wetland Emissions

8th February 2010. Geophysicists have long used subtle local variations in the earth’s measured gravity field to help build a picture of subsurface geological structures.  A team led by MethaneNet colleague Professor Paul Palmer at Edinburgh University has now pioneered a new use of gravity anomaly data to constrain estimates of methane emissions from different wetland areas (Bloom et al., 2010). They believe this new technique shows that increases in wetland methane emissions between 2003 – 2007 are largely due to warming of mid and high latitude regions.

The Edinburgh team used minute variations in the gravity field measured by the GRACE satellite to detect changes in wetland water table height. They then combined these data with NCEP/NCAR surface temperature information and correlated the results against atmospheric methane data from the Envisat satellite to infer wetland methane emissions.
When a sharp 2007 increase in global atmospheric methane concentration was recognised, the cause was not immediately apparent. No unusual changes in fossil fuel usage or biomass burning had occurred over that period. As wetlands are the largest single emitter of methane to the atmosphere, the attention of researchers logically turned to this source. Although this new gravity-based study attributes over 55% of the world’s natural wetland emissions of methane to tropical areas, it also strongly suggests that the recent increase arises from changes in boreal regions.
The work was also presented at the recent MethaneNet meeting (21-22nd January); it sparked a great deal of interest and a very lively discussion. Expect to hear more on this topic…
Reference: Bloom, A.A., Palmer, P.I., Fraser, A., Reay, D.S. & Frankenberg, C., 2010, Large-scale controls of methanogenesis inferred from methane and spaceborne gravity data, Science, 327, 322-325.