Journal Article 142M471B3J Carbon Dioxide Methane OP0UW79H66 methane emissions CO2 evasion Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. anthropogenic emissions atmospheric inversion benchmarking biosphere model bottom-up bottom-up models carbon stock change eddy covariance land-use change emissions natural emissions net CO2 flux observational constraints regional residual land uptake riverine carbon export source sectors terrestrial CO2 budget top-down top-down models wetland modeling