A109-02
A New Metric for Evaluating Northern Hemisphere Growing Season Net Flux in Climate Models
Friday, 11 December 2020: 04:18
Virtual
Morgan Cheatham1, Britton B Stephens2, Colm Sweeney3, Kathryn McKain4, Stephen Wofsy5, Roisin Commane6, Maryann R Sargent5, Prabir Kumar Patra7, Frederic Chevallier8 and Gretchen Keppel-Aleks9, (1)University of Michigan Ann Arbor, Ann Arbor, MI, United States, (2)National Center for Atmospheric Research, Earth Observing Laboratory, Boulder, CO, United States, (3)NOAA Global Monitoring Laboratory, Boulder, CO, United States, (4)NOAA ESRL Global Monitoring Division, Boulder, CO, United States, (5)Harvard University, Cambridge, MA, United States, (6)Columbia University in the City of New York, New York, NY, United States, (7)Center for Environmental Remote Sensing, Chiba University, Chiba, Japan, (8)LSCE Laboratoire des Sciences du Climat et de l'Environnement, Gif-Sur-Yvette Cedex, France, (9)University of Michigan Ann Arbor, Climate and Space Sciences and Engineering, Ann Arbor, MI, United States
Abstract:
Understanding terrestrial ecosystems and their response to anthropogenic climate change requires quantification of land-atmosphere carbon exchange. However, top-down and bottom-up estimates of large-scale land-atmosphere fluxes, including the Northern Hemisphere growing season net flux (GSNF), show significant discrepancies. Here, we develop a data-driven metric for the Northern Hemisphere GSNF from observations of atmospheric carbon dioxide (CO
2) concentrations collected during the HIAPER Pole-to-Pole Observations (HIPPO) and Atmospheric Tomography (ATom) flight campaigns. These campaigns sampled the atmosphere over the remote Pacific and Atlantic from ~80°N to ~60°S, attained vertical profiles from the marine boundary layer to an altitude of ~10 km, and spanned all seasons over a time period of nine years. We derived the Northern Hemisphere GSNF from these aircraft observations between 20-90N below a pressure ceiling of 300 hPa. This aircraft-derived metric is further refined using four independent inverse transport models to account for mixing at the southern and upper boundaries of our domain. Our method revealed the Northern Hemisphere GSNF to be -6.5 PgC/yr with less than 10% uncertainty.
We use this metric to evaluate net biosphere productivity from the Coupled Model Intercomparison Project (CMIP) Earth system models (phases 5 and 6). While the model-to-model spread in the biosphere component of GSNF has decreased relative to that of the (CMIP) phase 5 models, there is still disagreement on the magnitude and timing of seasonal carbon uptake with models both overestimating and underestimating the biosphere component of GSNF by as much as 5 PgC/yr. We further contextualize simulated net flux bias relative to our observational benchmark in the context of each model’s primary productivity and respiration fluxes. Our research shows that the flux inferred from these aircraft observations provides an additional constraint on large-scale, net fluxes in prognostic Earth system models that may ultimately improve our ability to accurately predict carbon-climate feedbacks.
