title: Towards robust regional estimates of CO2 sources and sinks using atmospheric transport models.
abstract: Information about regional carbon sources and sinks can be derived from variations in observed atmospheric CO2 concentrations via inverse modelling with atmospheric tracer transport models. A consensus has not yet been reached regarding the size and distribution of regional carbon fluxes obtained using this approach, partly owing to the use of several different atmospheric transport models. Here we report estimates of surface-atmosphere CO2 fluxes from an intercomparison of atmospheric CO2 inversion models (the TransCom 3 project), which includes 16 transport models and model variants. We find an uptake of CO2 in the southern extratropical ocean less than that estimated from ocean measurements, a result that is not sensitive to transport models or methodological approaches. We also find a northern land carbon sink that is distributed relatively evenly among the continents of the Northern Hemisphere, but these results show some sensitivity to transport differences among models, especially in how they respond to seasonal terrestrial exchange of CO2. Overall, carbon fluxes integrated over latitudinal zones are strongly constrained by observations in the middle to high latitudes. Further significant constraints to our understanding of regional carbon fluxes will therefore require improvements in transport models and expansion of the CO2 observation network within the tropics.
authors.affiliation: Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Kevin Robert
authors.initials: KR
authors.lastname: Gurney
authors.forename: Rachel M
authors.initials: RM
authors.lastname: Law
authors.forename: A Scott
authors.initials: AS
authors.lastname: Denning
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Rayner
authors.forename: David
authors.initials: D
authors.lastname: Baker
authors.forename: Philippe
authors.initials: P
authors.lastname: Bousquet
authors.forename: Lori
authors.initials: L
authors.lastname: Bruhwiler
authors.forename: Yu-Han
authors.initials: YH
authors.lastname: Chen
authors.forename: Philippe
authors.initials: P
authors.lastname: Ciais
authors.forename: Songmiao
authors.initials: S
authors.lastname: Fan
authors.forename: Inez Y
authors.initials: IY
authors.lastname: Fung
authors.forename: Manuel
authors.initials: M
authors.lastname: Gloor
authors.forename: Martin
authors.initials: M
authors.lastname: Heimann
authors.forename: Kaz
authors.initials: K
authors.lastname: Higuchi
authors.forename: Jasmin
authors.initials: J
authors.lastname: John
authors.forename: Takashi
authors.initials: T
authors.lastname: Maki
authors.forename: Shamil
authors.initials: S
authors.lastname: Maksyutov
authors.forename: Ken
authors.initials: K
authors.lastname: Masarie
authors.forename: Philippe
authors.initials: P
authors.lastname: Peylin
authors.forename: Michael
authors.initials: M
authors.lastname: Prather
authors.forename: Bernard C
authors.initials: BC
authors.lastname: Pak
authors.forename: James
authors.initials: J
authors.lastname: Randerson
authors.forename: Jorge
authors.initials: J
authors.lastname: Sarmiento
authors.forename: Shoichi
authors.initials: S
authors.lastname: Taguchi
authors.forename: Taro
authors.initials: T
authors.lastname: Takahashi
authors.forename: Chiu-Wai
authors.initials: CW
authors.lastname: Yuen