A spatially distributed model of methane emissions from Arctic tundra calculated from remotely sensed images and field data

Atmospheric methane concentration more than doubled over the last 200 years, after varying by less than 30% during the previous 10,000 years. In the past two decades the rate of this increase declined. To understand both the long-term increase in atmospheric methane, and its recent slowdown, more information about sources and sinks of atmospheric methane is required. Arctic tundra is a significant source of atmospheric methane, but the magnitude of this source is uncertain. Much of the uncertainty arises from the extrapolation of methane-emission measurements from field studies to large areas of tundra. For the present study, a spatially distributed approach for modeling methane emission from arctic tundra in the Toolik Lake area was developed. A regression tree that predicted methane-emission rates from values of environmental variables was developed from field measurements. The rules from this tree were used to combine images of environmental variables derived from ERS-1 SAR data, SPOT multispectral data, and a digital elevation model into an image of methane emission typical of the peak of the emission season. The average instantaneous methane-emission rate from the study area was estimated by the model to be 11 mg m{dollar}sp{lcub}-2{rcub}{dollar} d{dollar}sp{lcub}-1{rcub}{dollar}. This estimate is lower than some previous estimates of methane-emission from the North Slope of Alaska. The regression tree and images of environmental variables were also combined with annual methane-emission estimates to generate an image of annual methane emissions. The average annual methane-emission rate from the study area was estimated by the model to be 780 mg m{dollar}sp{lcub}-2{rcub}{dollar} yr{dollar}sp{lcub}-1{rcub}{dollar}. Annual methane emission from global tundra was estimated to be 12.2 Tg yr{dollar}sp{lcub}-1{rcub}{dollar} with uncertainty greater than 1 Tg yr{dollar}sp{lcub}-1{rcub}{dollar}.