Spatial Dependence of Uncertainty Explains Discrepancies Between Bottom-up and Top-down Estimates of Net Ecosystem Exchange
Kelsey T Foster, Stanford University/Carnegie Institution for Science, ktfoster@stanford.edu (Presenter)
Wu Sun, Carnegie Institution for Science, wsun@carnegiescience.edu
Anna M Michalak, Carnegie Institution for Science, michalak@carnegiescience.edu
To understand the biosphere's capacity to offset greenhouse gas emissions and to create policies that effectively address the impacts of climate change, we need accurate estimates of the carbon dioxide (CO2) exchange between the terrestrial biosphere and the atmosphere. Uncertainties persist in current estimates of net ecosystem exchange (NEE), as indicated by the large discrepancies between top-down estimates from atmospheric inversions and bottom-up estimates from terrestrial biosphere models (TBMs). Efforts aimed at reconciling these discrepancies have almost exclusively been focused at large aggregated scales (e.g., global and continental scales), which provides limited insights into reasons for the observed mismatches or where discrepancies are occurring. Here, we explore how the constraint provided by bottom-up vs. top-down methods varies as a function of spatial scale. We investigate the extent to which estimates from bottom-up models and top-down inversions are consistent across model ensembles and whether observed higher consistency across TBMs is representative of lower uncertainty in overall estimates.
By creating subsets of the model ensembles based on model agreement with large-scale constraints, we find that the observed greater consistency across ensembles of TBMs does not necessarily translate to lower uncertainty. Yet we show that selecting models based on consistency with atmospheric CO2 observations yields a set of models with converging flux estimates across TBMs and inversions. We further investigate what regions of North America show unambiguous discrepancies between bottom-up and top-down models and identify regions of North America that show statistically unambiguous discrepancies between inversions and TBMs. Our findings enable in-depth examination of the causes of discrepancies between top-down and bottom-up NEE estimates, which will ultimately lead to improved understanding of the terrestrial carbon balance.
Associated Project(s):
Poster Location ID: 3-21
Presentation Type: Poster
Session: Poster Session 3
Session Date: Thu (May 11) 3:00-5:00 PM
CCE Program: TE