Open AccessQuantifying the Terrestrial Carbon Feedback to Anthropogenic Carbon Emission
Author(s) -
Goodwin Philip
Publication year - 2019
Publication title -
earth's future
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.641
H-Index - 39
ISSN - 2328-4277
DOI - 10.1029/2019ef001258
Subject(s) - carbon fibers , environmental science , greenhouse gas , carbon cycle , climate change , global warming , atmospheric sciences , radiative forcing , ecology , ecosystem , materials science , physics , composite number , composite material , biology
The surface warming response to carbon emission is dependent on feedbacks operating in both the physical climate and carbon cycle systems, with physical climate feedbacks quantified via linearly combinable climate feedback terms, λ climate in watt per square meter per kelvin. However, land carbon feedbacks are often quantified using a two‐parameter description, with separate cumulative carbon uptake responses to surface warming, γ L in petagram of carbon per kelvin, and rising atmospheric CO 2 concentration, β L in petagram of carbon per parts per million. Converting the γ L and β L responses to an overall terrestrial carbon feedback parameter, λ carbon in watt per square meter per kelvin, has remained problematic, with λ carbon affected by significant nonlinear interactions between carbon‐climate and carbon‐concentration responses and a nonlinear relation between atmospheric CO 2 and subsequent radiative forcing. This study presents new relationships quantifying how the overall steady state terrestrial carbon feedback to anthropogenic emission, λ carbon , is dependent on the terrestrial carbon responses to rising CO 2 and temperature, β L , and γ L , and the physical climate feedback, λ climate . Nonlinear interactions between β L and γ L responses to carbon emission are quantified via a three‐parameter description of the land carbon sensitivities to rising CO 2 and temperature. Numerical vegetation model output supports the new relationships, revealing an emerging sensitivity of land carbon feedback to climate feedback of ∂ λ carbon /∂ λ climate ~ 0.3. The results highlight that terrestrial carbon feedback and physical climate feedback cannot be considered in isolation: Additional surface warming from stronger climate feedback is automatically compounded by reduced cooling from terrestrial carbon feedback, meanwhile around half the uncertainty in terrestrial carbon feedback originates from uncertainty in the physical climate feedback.