title: Variations in atmospheric CO2 growth rates coupled with tropical temperature.
abstract: Previous studies have highlighted the occurrence and intensity of El Niño-Southern Oscillation as important drivers of the interannual variability of the atmospheric CO2 growth rate, but the underlying biogeophysical mechanisms governing such connections remain unclear. Here we show a strong and persistent coupling (r(2) ≈ 0.50) between interannual variations of the CO2 growth rate and tropical land-surface air temperature during 1959 to 2011, with a 1 °C tropical temperature anomaly leading to a 3.5 ± 0.6 Petagrams of carbon per year (PgC/y) CO2 growth-rate anomaly on average. Analysis of simulation results from Dynamic Global Vegetation Models suggests that this temperature-CO2 coupling is contributed mainly by the additive responses of heterotrophic respiration (Rh) and net primary production (NPP) to temperature variations in tropical ecosystems. However, we find a weaker and less consistent (r(2) ≈ 0.25) interannual coupling between CO2 growth rate and tropical land precipitation than diagnosed from the Dynamic Global Vegetation Models, likely resulting from the subtractive responses of tropical Rh and NPP to precipitation anomalies that partly offset each other in the net ecosystem exchange (i.e., net ecosystem exchange ≈ Rh - NPP). Variations in other climate variables (e.g., large-scale cloudiness) and natural disturbances (e.g., volcanic eruptions) may induce transient reductions in the temperature-CO2 coupling, but the relationship is robust during the past 50 y and shows full recovery within a few years after any such major variability event. Therefore, it provides an important diagnostic tool for improved understanding of the contemporary and future global carbon cycle.
authors.affiliation: Division of Science and Environmental Policy, California State University Monterey Bay, Seaside, CA 93955, USA. weile.wang@nasa.gov
authors.forename: Weile
authors.initials: W
authors.lastname: Wang
authors.forename: Philippe
authors.initials: P
authors.lastname: Ciais
authors.forename: Ramakrishna R
authors.initials: RR
authors.lastname: Nemani
authors.forename: Josep G
authors.initials: JG
authors.lastname: Canadell
authors.forename: Shilong
authors.initials: S
authors.lastname: Piao
authors.forename: Stephen
authors.initials: S
authors.lastname: Sitch
authors.forename: Michael A
authors.initials: MA
authors.lastname: White
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Cristina
authors.initials: C
authors.lastname: Milesi
authors.forename: Ranga B
authors.initials: RB
authors.lastname: Myneni
mesh_terms: D001272:Atmosphere / Q000032:analysis*; D002245:Carbon Dioxide / Q000032:analysis*; D003198:Computer Simulation; D017753:Ecosystem; D059000:El Nino-Southern Oscillation; D004784:Environmental Monitoring / Q000379:methods / Q000706:statistics & numerical data; D005390:Fires; D005843:Geography; D008962:Models, Theoretical; D011891:Rain; D013696:Temperature; D013997:Time Factors; D014329:Tropical Climate
chemical_list: D002245:Carbon Dioxide
keywords: climate–carbon cycle coupling; global dynamic vegetation model; tropical land surface temperature