Assertion: methane's role | /r/HasProperty | discussed in large number of studies
Facets:
value: over the past years
type: TEMPORAL
value: controversially
type: MANNER
Source sentences:
text: The roles of both natural and anthropogenic sources, and variations in the atmospheric CH 4 sink, have been controversially discussed in a large number of studies over the past years, primarily centering around debate over biogenic versus fossil CH 4 sources.