Seminar: Atmospheric, Oceanic and Space Sciences

Title: Emergent constraints on the role of CO2 fertilization in the terrestrial carbon cycle

Presented by: Jet Propulsion Laboratory Research Scientist David Schimel

Date: Friday, November 15
Time: 1:30 PM to 2:30 PM
Location: Space research building auditorium, room 2246

Abstract: Feedbacks from the terrestrial carbon cycle will mitigate or exacerbate future climate change, yet the sign and magnitude of these feedbacks are poorly known.  The magnitude of negative feedback from CO2fertilization has been particularly difficult to constrain with observations, complicated by the atmospheric signal of forest regrowth after clearing. Theory and experiments lead to a prediction of CO2 fertilization scaled to plant productivity, with a global maximum in the tropics.

The CO2 fertilization hypothesis appears to be contradicted by interpretations of atmospheric CO2 measurements showing high mid-latitude and low tropical uptake.  Here we use a new approach to the joint analysis of atmospheric and ecosystem data to show evidence for tropical sinks supporting a long-hypothesized negative terrestrial feedback to CO2 and climate, providing a constraint on modeled terrestrial feedback.  Integration of atmospheric, in situ and simulation analyses suggest a significant tropical uptake not associated with forest regrowth or other disturbance processes, suggesting a present-day tropical CO2 fertilization effect of 1.3 +/- 0.6 Pg C y-1.