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

A Department of Atmospheric and Oceanic Sciences seminar presented by Dr. David Schimel, Senior Scientist, Jet Propulsion Lab, California Institute of Technology

Wednesday, November 20, 2013
3:30 PM
MSB 7124

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 CO2 fertilization has been particularly difficult to constrain with observations, complicated by 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 show global 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 CO2fertilization effect of 1.3 +/- 0.6 Pg C y-1.  This implies a significant role for terrestrial negative feedbacks in the modern carbon cycle and provides a strong constraint on models.

SEMINAR at 3:30 PM
SEMINAR TEA:  4:30-5:00PM (MSB 7124B)